[jmfitamant]

Greatings from Québec !

I was very impressed by the photographies made with a 300 mm Borg DG 60 ED. Its conception seems to be very different than traditionnal telephotos.

Is there someone (birdwatcher, for example) who uses this lens and could share his feelings about it ? Is there one review somewhere on it ?

http://www.sciencecenter.net/hutech/birding/index.htm

Thanks for your help.



jmf

[Guest]

[quote name='jmfitamant' timestamp='1294533762' post='5396']

Greatings from Québec !

I was very impressed by the photographies made with a 300 mm Borg DG 60 ED. Its conception seems to be very different than traditionnal telephotos.

Is there someone (birdwatcher, for example) who uses this lens and could share his feelings about it ? Is there one review somewhere on it ?

http://www.sciencecenter.net/hutech/birding/index.htm

Thanks for your help.



jmf

[/quote]



Greetings from Germany,



Telescopes are a cheap alternative if you are willing to live with its drawbacks. My own experiences are that in a lot of cases, the massive increase in focal length can compensate for a lack of sharpness. I owned an AF-S 80-200/2,8 and used it with a Kenko DG 1,4x TC, resulting in 280mm focal length. Even stopped down to f/8, the photos I got with a modified Bresser Messier 1000/102 simple achromat beat it multiple times. But usability is a different thing. I cannot imagine taking the achromat to the zoo, for example. Weighting 7kg, it is a hefty load and big as well, measuring over a meter. Tripod requirements are high, increasing the load further.



If you are interested, I can dig for some test shots with the telescope to give you an impression about the performance.



Christian

[genotypewriter]

[quote name='TheChris' timestamp='1294652362' post='5401']

Telescopes are a cheap alternative if you are willing to live with its drawbacks. My own experiences are that in a lot of cases, the massive increase in focal length can compensate for a lack of sharpness. I owned an AF-S 80-200/2,8 and used it with a Kenko DG 1,4x TC, resulting in 280mm focal length. Even stopped down to f/8, the photos I got with a modified Bresser Messier 1000/102 simple achromat beat it multiple times.

[/quote]

Sounds interesting, Christian... what I've always wandered is whether the telescopes with any built-in focusing mechanism allow for the sorts of close focusing that we do for terrestrial photos?



GTW



EDIT: wondered* lol

[popo]

[quote name='genotypewriter' timestamp='1295074423' post='5523']

Sounds interesting, Christian... what I've always wandered is whether the telescopes with any built-in focusing mechanism allow for the sorts of close focusing that we do for terrestrial photos?[/quote]

Even around infinity, telescopes need accurate focusing too. And if you need to get closer than it allows, you just use the standard macro trick of moving the camera away like with extension tubes.



Just for fun, I did see how close my Nexstar 4SE could focus (1325mm f/13). I managed as close as 3m for a magnification of 0.6x <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' /> It could almost work as a long working distance macro if I had any way to hold it steady enough in the field...



Back on the original topic, I did also wonder about astrographs doubling as a terrestrial long focal length manual lens. The main concern I had was although most are highly colour aberration corrected for their normal use at infinity, I wonder if that also applies at significantly closer focus distances? Consider that photographic lenses of a similar specification will typically have far more optical elements.

[genotypewriter]

[quote name='popo' timestamp='1295087051' post='5526']

Even around infinity, telescopes need accurate focusing too. And if you need to get closer than it allows, you just use the standard macro trick of moving the camera away like with extension tubes.

[/quote]

That's a scary thought... to add that many extension tubes!





[quote name='popo' timestamp='1295087051' post='5526']

Just for fun, I did see how close my Nexstar 4SE could focus (1325mm f/13). I managed as close as 3m for a magnification of 0.6x <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' /> It could almost work as a long working distance macro if I had any way to hold it steady enough in the field...



Back on the original topic, I did also wonder about astrographs doubling as a terrestrial long focal length manual lens. The main concern I had was although most are highly colour aberration corrected for their normal use at infinity, I wonder if that also applies at significantly closer focus distances? Consider that photographic lenses of a similar specification will typically have far more optical elements.

[/quote]

Needless to say, they won't be optimised for the close distances but for the sorts of terrestrial distances one would use a 1300mm lens for shouldn't be that far from infinity, so any performance drops should be minimal. I'm of course, not referring to macro or close-ups... just things like long distance sceneries, etc.



However, I don't expect bokeh to be particularly smooth. Any comments from your experience?



GTW

[popo]

[quote name='genotypewriter' timestamp='1295094193' post='5531']

That's a scary thought... to add that many extension tubes![/quote]

It might not be that bad! I achieved my example with only the built in focusing, which went quite a lot closer than the manufacturer's spec claimed.

Needless to say, they won't be optimised for the close distances but for the sorts of terrestrial distances one would use a 1300mm lens for shouldn't be that far from infinity, so any performance drops should be minimal. I'm of course, not referring to macro or close-ups... just things like long distance sceneries, etc.



However, I don't expect bokeh to be particularly smooth. Any comments from your experience?

I should add the scope I tried is a mirror design, whereas the original post was more about refractors. In general, refractors are shorter focal lengths and should behave similarly to a photographic lens. For example the model mentioned is 300mm f/5. Not that exciting in photograph lens terms. I guess at astronomical distances you don't usually have to worry about bokeh... so I have no idea what they might do there.



I only did a few test shots on my mirror scope terrestrially. It wasn't practical in any way due to a combination of factors, not least that fixed f/13 is already softened by diffraction and in daytime the air was never that stable! Beyond a few hundred meters or so it gets quite wobbly.

[genotypewriter]

[quote name='popo' timestamp='1295115945' post='5538']

For example the model mentioned is 300mm f/5. Not that exciting in photograph lens terms. I guess at astronomical distances you don't usually have to worry about bokeh... so I have no idea what they might do there.[/quote]If it's a mirror design with good contrast then it's likely produce the donuts like normal mirrors. In a lot of cases it's not that bad.





[quote name='popo' timestamp='1295115945' post='5538']

I only did a few test shots on my mirror scope terrestrially. It wasn't practical in any way due to a combination of factors, not least that fixed f/13 is already softened by diffraction and in daytime the air was never that stable! Beyond a few hundred meters or so it gets quite wobbly.[/quote]

Yes, the atmospheric turbulence get in the way of long lens IQ... quite a pain <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />





GTW