Dobsonian telescopes? (1 Viewer)

[Tord]

Hi

After seeing what can be achieved with refractor scopes, a fellow photographer asked me if a Dobsonian scope could be used for wildlife/bird photography.

E.g. this scope that he acquired recently for astrrophotography, and what adapters would be required.

Could anone here answer his question?

Thanks,
Tord

 

[etudiant]

Dobsons were initially designed to allow a big mirror to perform in a cheap mount.
For daytime use, the big mirror does not buy much, as haze and heat effects often mess up longer range imaging where the big glass would be most useful.

The practical challenges include:
1: the pointing and tracking of a bird with a big dobsonian scope is quite difficult.
You would want some sort of wide angle finder, maybe a red dot or Telrad, just to get to the right area. Then the detail spotting will still be clumsy, because the scope needs separate corrections on 2 axes to stay on target.
2: the need to mount photography gear to the eyepiece messes up the balance of the scope as well as take the place a Telrad would use. So the job gets harder.

That said, you should be able to use this scope for birds that stay stationary such as owls or move mostly in one plane (shorebirds for instance). Nesting birds might also be good targets. The light bucket capacity of the dobson would shine for low light situations.

 

[Hor Kee]

Not to mention that it will be a monster to cart around while chasing small birds all over the countryside!

 

[cango]

That said, you should be able to use this scope for birds that stay stationary such as owls or move mostly in one plane (shorebirds for instance). Nesting birds might also be good targets. The light bucket capacity of the dobson would shine for low light situations.

Is a Dobson similar to a mirror lens, regarding bokeh?

 

[Tord]

Dobsons were initially designed to allow a big mirror to perform in a cheap mount.
For daytime use, the big mirror does not buy much, as haze and heat effects often mess up longer range imaging where the big glass would be most useful.

The practical challenges include:
1: the pointing and tracking of a bird with a big dobsonian scope is quite difficult.
You would want some sort of wide angle finder, maybe a red dot or Telrad, just to get to the right area. Then the detail spotting will still be clumsy, because the scope needs separate corrections on 2 axes to stay on target.
2: the need to mount photography gear to the eyepiece messes up the balance of the scope as well as take the place a Telrad would use. So the job gets harder.

That said, you should be able to use this scope for birds that stay stationary such as owls or move mostly in one plane (shorebirds for instance). Nesting birds might also be good targets. The light bucket capacity of the dobson would shine for low light situations.

Thanks!

I will forward this useful information.

Cheers
Tord

 

[etudiant]

Is a Dobson similar to a mirror lens, regarding bokeh?

Presumably, although that is just an uninformed guess.
My only use of dobsons has been for visual observation of stars and landscape objects.

The dobson is just a big mirror lens in photography use, but maybe size matters for bokeh.

 

[Paul Corfield]

You would likely get some sort of donut bokeh from the small secondary mirror blocking part of the image and maybe some other strange looking bokeh besides the donuts. Contrast would be poor in the photos compared to a refractor design.

Paul.

 

[Tord]

Hi,

The guy I mentioned got hold proceeded with the adapters needed to mount his DSLR on his Skywatcher Skyliner-200P . Attached is a sample that he shared and gave permission to upload on this site.

Sharpness, contrast colors and background look good to me.

Feedback most welcome.

/Tord

 

[Paul Corfield]

I guess we would need to see a range of photos in various situations to see if it would produce donut bokeh. Out of focus highlights tend to produce it the most, like sunlight sparkiling on water or highlights on blades of grass. This photo looks fine though. Might be ok in a static set up but certainly not a portable scope.

Paul.

 

[Tord]

Agree, at 20kg+ the setup is hardly portable. He intends to deploy it close to his car for more static application areas.

 

[richardlongley]

Hi,

I am the individual (will not yet call myself photographer) who took the goldfinch shot.

From my experience so far the advantage may be the shutter speed possible and extreme distances due to the extreme light gathering at f/6 and 1200mm. I hope to take it to a nearby lake this weekend.

As already highlighted, it clearly is not going to be a portable device. It is afterall designed to be used stationary. I don't think anyone could ever use this as their only lense, but it just might be a useful tool to have available.

I will report back if I manage to get out this weekend.

 

[FineArt]

That is the same scope I got. It works well once you get used to using it.

 

[FineArt]

I guess we would need to see a range of photos in various situations to see if it would produce donut bokeh. Out of focus highlights tend to produce it the most, like sunlight sparkiling on water or highlights on blades of grass. This photo looks fine though. Might be ok in a static set up but certainly not a portable scope.

Paul.

Bokeh can get ugly. Be ready to focus stack.

 

[DanC.Licks]

I used to have a really good 8" Dob, and you could take pictures with it if things were not moving around. Sharp....WOW! and ZERO CA! But as with all really long lenses, air is the biggest villain.