1200mm telescope - progress made, more work needed

[richardlongley]

I have posted on other threads regarding the possibility of using my dobsonian telescope for wildlife photography.

I had a play today and found I made progress. If I can use this telescope as a lens, then it could be an incredibly powerful thing.

Below is a picture taken at 300mm on my E3. Ignore the lack of quality, it is purely to put a perspective on the 2nd picture.



the 2nd pic is taken with my 1200mm telescope, and with my e410 hand held hovering above the viewer, plus with a 2x adaptor fitted. In affect this makes the telescope 2400mm
You can see a huge amount of light pollution, this is due to the fact that I am holding the camera above the telescope viewer, with around 10-15cm of 'space' between them.
Do you think this has legs? I kno you can buy specialised adaptors to put a camera on this telescope, but I am not sure they would allow me to focus at anything much less than infinity. The rake in this picture was about 8m away.

[Tordan58]

Re: 1200mm telescope - progress made, more work needed

Hi Richard,


The picture is sharp as far as I can see as far as the lower part is concerned, the sticker texture is clearly visible. I suppose you held the camera somewhat titled and not at square angle.

It lacks some contrast but has no CA as far as I can see. And the bokeh looks OK.

Trying to figure out - did you mount a EC20 on the camera or on the scope? What lens did you use, if any?

Do you have a pointer to the scope you are using? Or a specification? This would be useful to provide guidance regarding what adaptors to use.

/Tord

[richardlongley]

Re: 1200mm telescope - progress made, more work needed

Hi Tord

this is what I used

Skyatcher Skyliner 200P http://www.telescopehouse.com/acatalog/info_10717.html

With various attachments onto the viewfinder, to create the longest column I could.

Then my E-410 hand held (so you will be correct about the angle distortion) above the viewfinder.

The viewfinder has lenses to sit on the mount, I used it without a lens, and so used the camera and set up below to converge the light onto the sensor:

E-410
EX-25
4/3 mount converter
2x converter - This was the only 'glass' between the scope and the camera sensor - like this one http://www.ebay.co.uk/itm/KEPCOR-AUT...item2a17211c1f

In affect, what I did was use the 2x converter as the lens to focus the image onto the sensor. I focused by moving the camera towards, and away from the scope.


If I get more extension tubes, I can adjust the focus from the viewfinder.

I hope to get an EC14 soon, and that may be better, with the EX25 and possibly some cheap extension tubes.

[Tordan58]

Re: 1200mm telescope - progress made, more work needed

Hi,

Wow, 1200 mm, F/6 is respectable. I have used such long focal length when digiscoping with my Nikon 82mm spotting scope, which provides 1200mm as well, but the performance is only F/12.8.

I have no experience about Dobsonian scopes but what I guess you should do is to find a way to add extension tubes to the focuser to bring the camera focuing plane at a useful (practical) distance, and firmly mount it to the camera body.

Having read the spec it seems the scope is fitted with a 2" Crayford focuser. What you will need is probably something like this;

(Additional extension tubes e.g. 80 mm length)
Adapter 2" to T2
T2 Adaptor Ring for Cameras with Four-Thirds (4/3) Bayonetthis one. Cost 20$.

Lastly, you could add the EC14 or EC20 for extra magnification. Try first without.

Hope this helps
Tord

[Bikie John]

Re: 1200mm telescope - progress made, more work needed

Richard - a good UK source of adapters and extension tubes is SRB-Griturn - http://www.srb-griturn.com/ . I am not sure about a 2 inch to T-mount adapter, but you can certainly get a set of T-mount extension tubes and a manual-only T-to-4/3rds adapter. They are very helpful if you ring them up for advice.

As Tord says, this will let you mount the camera rigidly on the scope and will also avoid stray light getting in.

Good luck ... John

[Tordan58]

Re: 1200mm telescope - progress made, more work needed

I second what John writes, SRB Griturn is an excellent supplier (I have purchased digiscoping accessories from them). Only reason for me not mentioning them in the first place is that I am based outside the UK, so Germany or UK does not really matter for me.

Another hint. 4/3 mounts can sometimes be difficult to find (that was the case when I purchased the accessories to my scope). Should that happen to you, then a viable and somewhat longer path is to buy e.g. Canon or Nikon mount and adding an adapter ring closest to the camera body.

/Tord

[richardlongley]

Re: 1200mm telescope - progress made, more work needed

Thanks guys.

Regarding glass / EC14 etc.

So, if I use my EX25, then put in an EC14 will that work as a kind of AF confirm chip?? Sorry much of this is new to me.

Then the extra extension tubes, T2 mounts and I should be sealed and enough extension to bring in a focus?


One thing this set up will allow is fast shutter speeds. The dobs' scopes are known as light buckets.
The dissadvantage is going to be how big the set up is. Not something for you to keep in your car 'just in case'!!
I can see a real opportunity for it when the target is at a distance but in a predictable position.

The scope is one of the most powerful that you could put in the back of your car and travel with,,,,,, and it sets up quickly, is not too heavy, but it is still the size of a small person!

[richardlongley]

Re: 1200mm telescope - progress made, more work needed

Richard - a good UK source of adapters and extension tubes is SRB-Griturn - http://www.srb-griturn.com/ . I am not sure about a 2 inch to T-mount adapter, but you can certainly get a set of T-mount extension tubes and a manual-only T-to-4/3rds adapter. They are very helpful if you ring them up for advice.

As Tord says, this will let you mount the camera rigidly on the scope and will also avoid stray light getting in.

Good luck ... John

Thanks John,

I am travelling down to the M1 tomorrow, so I may be able to call in and speak to them.

Regards
Richard

[Tordan58]

Re: 1200mm telescope - progress made, more work needed

Thanks guys.

Regarding glass / EC14 etc.

So, if I use my EX25, then put in an EC14 will that work as a kind of AF confirm chip?? Sorry much of this is new to me.

Richard,

What you need is the following, starting from the scope focuser and towards the camera body:

• 2" extension tube to allow to focus on objects at useful distance (being able to focus on closer objects). For my 600mm scope I found 80mm extension tube to be right, it allows me to focus down to ~4 meters while still being able to focus on infinity, not sure how much you will need. Note: 2" is the diameter of the fitting.
• Adapter from 2" to M42
• Adapter from M42 to 4/3 fitting
• Optional, for extra magnification, the EC14/EC20. Try first without it.

You can forget about the EX25 to start with (or use it as an extra extension tube)

Regarding the AF confirm chip, this is optional. I will try to explain.
AF confirm chips were introduced to help using legacy lenses that have no AF. They measure the contrast and when contrast is maximal they generate an electrical output signal that "fools" the camera, appearing as an AF lens that has locked focus, and causing the green light to appear in the viewfinder and the audible beep signal.

The idea is to be able to use not only legacy OM lenses, but all lenses. E.g. prime Zuiko, Nikon, Canon lenses...

To use these lenses you need a mechanical adapter between the lens and camera body. E.g. OM -> 4/3, Nikon -> 4/3, Canon -> 4/3 etc.

The chip has a connector with an interface that is specific for the system you are using e.g. 4/3. The chip is mounted (glued) in the inside of the adaptor and positioned so that the connector is aligned with the contacts on the camera body. Open the link that I provided in previous post and you will see what I mean.

Some AF chips can be programmed, allowing to set the focal length and lens speed, which will be stored in the EXIF data. The one I linked to is programmable.

Thanks guys.
Then the extra extension tubes, T2 mounts and I should be sealed and enough extension to bring in a focus?

Sealed? If you mean secured, providing a firm mechanical connection, then the answer is Yes. Again, not sure how long extension tube you will need. It depends on how close subjects you plan to photograph. With the extreme 1200mm focal length, possibly 1700/2400mm with EC14/EC 20 I would guess that you are intending to photograph at a closest distance of 25/35/50 meters or more.

Thanks guys.
One thing this set up will allow is fast shutter speeds. The dobs' scopes are known as light buckets.
The dissadvantage is going to be how big the set up is. Not something for you to keep in your car 'just in case'!!
I can see a real opportunity for it when the target is at a distance but in a predictable position.

The scope is one of the most powerful that you could put in the back of your car and travel with,,,,,, and it sets up quickly, is not too heavy, but it is still the size of a small person!

I agree. F/6 is an impressive lens speed considering the focal length. If you add the EC14 you will lose 1EV (F/8.4 which is still quite OK) and the EC20 will cause a 2EV penalty (F/12, which starts to become tricky to focus due to the dark viewfinder).

What you will achieve provided you get the bits and pieces together is an impressive setup that if I were you I would deploy at a good location, withing close walking distance from the car. A hide/platform/tower/hill...

To give you an idea about the specs I made some quick calculations;
1200 mm is 0.6 degrees horizontal angle of field on 4/3 system

Say the subject is a amammal with a size of 1 meter. You will be able to take full frame captures at 54 meters distance. At same distance, a medium sized bird, 25 cm, will occupy 1/4 of the frame which is nou too bad. Hope you are following...

For reference here is a picture of a fox at 300 meters distance, taken through the 1200 mm scope and with 2X zoom on a cheapish P&S camera (i.e. ~2400 mm FL)

/Tord

[richardlongley]

Re: 1200mm telescope - progress made, more work needed

Richard,


What you need is the following, starting from the scope focuser and towards the camera body:

• 2" extension tube to allow to focus on objects at useful distance (being able to focus on closer objects). For my 600mm scope I found 80mm extension tube to be right, it allows me to focus down to ~4 meters while still being able to focus on infinity, not sure how much you will need. Note: 2" is the diameter of the fitting.
• Adapter from 2" to M42
• Adapter from M42 to 4/3 fitting
• Optional, for extra magnification, the EC14/EC20. Try first without it.

You can forget about the EX25 to start with (or use it as an extra extension tube)

/Tord

Thanks Tord,

Actually I think I may have some of this as part of my telescope. What I plan on doing is taking the tubes that I already have with my scope, and my camera with me to the shop John recommended.

I understand the consideraation of size/magnificnation etc - thanks for the help and support.

I think your right about distances, The picture at the start of this thread shows the power. I would only get part of the head of a fox (for example) at that distance.

It could be interesting to use it for garden birds - the advantage being I could focus on the feeder, and get soem extreme close ups of birds heads!!


I'll keep you informed of progress- once again thanks for all your help.

Regards
Richard

[Tordan58]

Re: 1200mm telescope - progress made, more work needed

Thanks Tord,

I'll keep you informed of progress- once again thanks for all your help.

Regards
Richard

No problem, just drop a line anytime and I will be happy to assist.

Looking forward seeing some results.

/Tord

[Graham_of_Rainham]

Re: 1200mm telescope - progress made, more work needed

A while back I put my 600mm Sigma with a 2x converter onto an E-500 that effectively gave me a 2400mm reach. I did try putting a 1.4 on as well to give me 3360mm but the light transmission was only ever enough on VERY bright days.

This truck is four to five hundred yards away

[Tordan58]

Re: 1200mm telescope - progress made, more work needed

Hi Graham,

600mm X2 is 1200mm. I suppose you mean "equivalent to 2400mm on 35 mm system"?

/Tord

[richardlongley]

Re: 1200mm telescope - progress made, more work needed

When we talk about the reach

I guess that if we are modifying the scope to focus far behind the intended viewfinder, we are further increasing the focal length.

If I have a 1200mm scope, and I focus the image 200mm behind the viewfinder, then I am at 1400mm.

Then add in the 2x converter and it is 2800mm (equivalent to 5600mm)??? Does that sound right???


To give you an idea as to why they call these scopes 'light buckets' - the scope has an internal diameter of 200mm (the 200p). If we compare that to our specilised lenses of 52-76mm for example.

Of course the light gathering is proportional to the square of the diameter, so if we move from a 58mm lense to this 200P, we are gathering around 11 times as much light (again I hope that makes sense and my understanding is correct)
It is this amount of light that I hope will allow me to magnify the image so much and still get enough light to have fast shutter speeds


Regards
Richard

[Graham_of_Rainham]

Re: 1200mm telescope - progress made, more work needed

Hi Graham,

600mm X2 is 1200mm. I suppose you mean "equivalent to 2400mm on 35 mm system"?

/Tord

Indeed