Camera lens vs telescope ? (1 Viewer)

Over six months ago, I thought I was going to purchase a Televue TV-85 for the purpose of photographing distant birds with my DSLR. At the time my longest camera lens was a 400mm. Through a series of fortunate events, I was able to purchase a Canon 500mm f4 lens and have been using it since for photographing a variety of subjects but mostly birds. Frequently I use it with a 1.4x converter, making it a 700mm f5.6. But distant birds are still a challenge to photograph and even by adding a 2x TC and then stacking that with a 1.4x, I'm getting essentially a 1400mm f11 and even with the superb quality of the Canon lens, images at that distance are mediocre at best... I'm guessing because of the number of elements involved

If I understand what I read on this forum correctly, I can invest in say a reasonably good Orion 80 ED APO refractor with a (photographic)focal length equivalent of 600mm and with the addition of several decent Barlows or even stacking the same combination of TCs I use with my lens easily achieve that 1400 or beyond with better image quality.

It seems too good to be true so I have to ask: what am I missing here?

Chris

Hello Chris,

I do not know about comparison of the two options and their image quality. So I will not comment on that.

One thing is that heat, humidity can distort the images over long distances - So I doubt that you will get much more than mediocre images over big distances, unless climatic conditions are perfect.

Nice images on your website by the way...

Do you have any examples of what you call mediocre with the 500/1400mm??

kurakura said:

Nice images on your website by the way...

Do you have any examples of what you call mediocre with the 500/1400mm??

Click to expand...

No, nothing for "public consumption"... recent results were so disappointing, I ended up wiping the card clean!
In my most recent attempt where the conditions were acceptable with virtually no wind and using an ISO of 800, and doing all the right things (camera (7D) and lens+TCs locked firmly on the tripod, mirror lockup and remote shutter release), manually focusing on an osprey nest at a distance of roughly 500', results were poor.

The attached image was made with the 500+1.4 under the same conditions, and worked out fine so I figured it must have been adding the additional glass:

A 500mm f4 lens is basically a highly corrected 5" refractor. The typical 3" refractor used in digiscoping will have a hard time keeping up with the resolution of the larger lens. Still, small targets like birds at 500ft is a challenge for ANY camera lens combo to get consistent IQ results, including digiscoping. Getting within 300ft or less should be your goal if you want to print/publish anything better than record shots.

I'm not a Canon expert but I also think that stacking TCs works best on the Ds body. Especially the AF. Probably best to check with the pros on birdphotographers.net and naturescapes.net.

Chris, others have answered most if not all your questions. The 80ED will not perform better than your 500mm f4. The other option would be the longer FL Triplet (higher quality built type instead of cheap ones). That would give you the advantage of lesser glass than your numerous stacking of glasses. Your greatest enemy would still be the atmospheric distortion which will be highly magnified with longer FL. Your best bet would be to shoot early, just after getting enough light and before evaporation of liquid increases. Also try shooting further away from ground. The first 6-8' off the ground will have the highest atmospheric distortion from evaporation.

Thank you all for your responses!

Lots to think about but mostly I guess I'll just start saving up for the Canon 800mm 'cause that appears to be my best bet...

Chris