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richardlongley
7th July 2012, 09:30 AM
moved from the photo forum:


OK,

In between thunder storms and in very poor light I set up the 1200mm early evening and with my extension tubes.

These are the results. focusing on the top of a chimney I guess just about 100 yards away (maybe less difficult to tell).

for comparasin I started with my 70-300mm and then moved onto my 1200mm scope. All pics are taken with my E3, and I tried to keep some parameters the same to give a real comparasin.

70mm ISO200 1/350s and f/5.6
http://i90.photobucket.com/albums/k273/bantamweight1911/70mm1of1.jpg

300mm ISO200 1/350s and f/5.6
http://i90.photobucket.com/albums/k273/bantamweight1911/300mm1of1.jpg

the 1200mm with no magnification, so
1200mm,, ISO320 1/350s
http://i90.photobucket.com/albums/k273/bantamweight1911/1200mmwith2xpentax1of1-1.jpg





the 1200mm with 2x pentax
2400mm ISO640 1/350s

http://i90.photobucket.com/albums/k273/bantamweight1911/1200mmwith2x1of1.jpg
The light wasnt good enough to use the multipliers really, although maybe useful in bright conitions. I want to try the olympus EC14, as I think that could be an optimum.

Finally to further evaluate the shot at 1200mm and 2400mm, I cropped the 300mm shot to a similar detail level:
http://i90.photobucket.com/albums/k273/bantamweight1911/300mm1of1-3.jpg
I think it is clear that the 1200mm has the potential to capture detail at distances, but it may need goo dlight to get sharp pictures.


If we get any fair weather over the weekend I will try to get some shots of birds,,,,,,, but that is probably wishfull thinking


The problems are:
The weight of the camera spoils the balance of the scope, and I will need to use something like a bag of rice to counterbalance.
The DOF seems quite shallow to me, and it can be tricky to find targets because if you are not focused you just cant see it!
I think shake is a big problem, so high shutter speeds will be required - again good light needed.

richardlongley
7th July 2012, 09:44 AM
Tord suggested trying to capture an object with details at a distance of 50m with light reflecting from it (i.e. sun behind photogropher).

This isnt possible today, but I have taken a couple more pictures, whicih have been edited a little in LR.

The first is a couple of Jackdaws on top of the same roof seen above. (on the roof furthest away, so I guess around 100m. Far from ideal as the sky behind is completely white, and the roof and birds are very dark. Still this is a picture that would not be possible with my 70-300mm lens

Note the camera settings - ISO 640 s1/1500 (so light gathering is really great) cropped around 60%
http://i90.photobucket.com/albums/k273/bantamweight1911/jackdaw1of1.jpg
Not great in terms of sharpness or contrast, but I am asking a lot of the camera/lens here. This is not a photograph I would take and expect to produce a worthwhile image.




The 2nd photo today is my attempt to assess the contrast and sharpness. I placed this trainer as far away as I could on a tripod at the bottom of my garden. This is around 30 metres away, completed shaded, and with a dense hedge around 2 metres further back behind the trainer. Not cropped, but edited very slightly in LR
ISo640 1/350s
http://i90.photobucket.com/albums/k273/bantamweight1911/trainer1of1.jpg
this is quite sharp, but could be better, and still lacks some contrast.

richardlongley
7th July 2012, 01:37 PM
I think this picture highlights what the problem is going to be, but also the advantages that may be available.

I focused the scope at around 10-11 m at a bird feeder. I had to move the scope away from the feeder to be able to focus so 'close'

I focused on the bird feeder, and got this pic. Clearly the bird is slightly out of focus, but the bird feeder sharpness and contrast I think is very good. This was in good light.

ISO 320 1/750 s
http://i90.photobucket.com/albums/k273/bantamweight1911/dunnock1of1.jpg
I didnt do a lot in LR, just sharpened it very slightly

richardlongley
7th July 2012, 03:16 PM
Here is the set up

note :

1. I still need more extension tubes to focus at 10 metres. Each connection is left slightly unscrewed to maximise the extension

The extensions are:
EX 25 - 25mm Olympus extension tube
4/3 to M42 conversion
M42 extension tubes,
Standard T fitting scope extension tube
viewfinder


2. The weight of the camera causes the scope to drift, I corrected this with a piece of wood!

http://i90.photobucket.com/albums/k273/bantamweight1911/P7070506.jpg


http://i90.photobucket.com/albums/k273/bantamweight1911/P7070505.jpg

Tordan58
8th July 2012, 09:07 AM
Hi Richard

How was focusing? Quite easy with F/6 I suppose?
How was the operation, having to operate at square angle? Tricky?

Some feedback:

At 1200mm F/6 your setup will have a very shallow DOF. To give you an idea I quickly checked in DOF master. (Used F/5.6, closest value).
At 10 meters: Less than 1 cm
At 15 meters: A few cm
At 30 meters: In the magnitude of 10 cm
At 100 meters: In the magnitude of a meter

Above meaning that for practical applications there is little point in aiming at distances as close as 10 meters.

I think the bird on the feeder has some motion blur if you look at the head, the shoulders and wings look sharp though.

The bokeh is OK (shoe picture). Could you share a picture with a background having light parts to check presence of any "donuts". Similar compostision but with light reflections on foilage.

The contrast is somewhat poor, which should be expected with a dobsonian scope I have read. Can be fixed in SW. Not bad, though.

Pictures you have shared look somewhat underexposed, 1/3 or 1/2 EV. Perhaps you should compensate in camera.

Colors look OK, I think they show a tad pink hue but not much, easily fixed in SW.

The weight balance needs to be fixed with a counterweight as you have noticed.

I will share some pictures with my 600mm refractor scope + EC20 as comparison.

Cheers
Tord

richardlongley
8th July 2012, 09:24 AM
Hi Tord,

Thanks for your feedback / advice.

Some additional comments / reactions.

Have you seen the pic in the photo forum? I got a nice picture of a pigeons head, showing that focusing is possible.


I really dont think the secondary mirror will be a problem at all.. I say this for several reasons:
1. It isnt a problem when looking with the naked eye, or with the eyepieces. I have clearly seen the spot of jupiter through this scope.
2. The diameter of the sec. mirror is very very small compared to the primary mirror.
3. I was sent an article about the lack of affect on picture quality from small marks on a lens

4. From using the scope and camera, the 2 problems are focus and shake (as shown in the bird picture)
Your calcualtions on DOF are exactly right from my experience
5. At 1200mm, the shake is the BIG problem. In live view, or through the eyepiece the picture quality is really excellent.
HOWEVER - when I zoom in 7x on live view I can see how much the picture is moving, it is NEVER completely still.

I think I need to use shutter speeds of 1/750 or faster, and probably 1/1000 or faster (even for stationary or slow moving subjects). This may force me to use high ISO in most lights.



I am starting to think that in the end the result will be that I do not use this scope for wildlife photography - but it is a great learning exercise, and if I ever want a picture of something at a huge distance then this would be as good as you could get (without spending 2000)