Some digiscoping experiments with a dslr (1 Viewer)

[bluedubius]

Jules,

Thanks for taking time to set this up. I think it will provide some very interesting and useful observations (the beginning point for all good science). Looking forward to participating with my Celestron 80ED refractor. I still can't achieve focus without using an extension tube, but I can include that in my summary data.

Rick Phillips
(not the same Rick)

 

[vkalia]

Yeah but your "data" in this case comes from bad science. I think if you want to have "fun" testing optical configurations, posting nature pics is just as valid as your protocol to determine what works and what doesn't. But to put this protocol out as some kind scientific study is ludicrous. Sorry for being so direct.

Rather than being sorry for being direct, you should be sorry for being incorrect.

The goal of this is to have some data to compare the real-world quality of the results gained with various configurations of refractors + barlows + TCs + spacers. And this test is going to perform that very well. Depending on the results, we may choose to perform additional testing to eliminate more variables if so required. It is a fairly sound, repeatable method of field-testing by *photographers* (as opposed to measurement wonks). In other words, it is scientific enough for the purpose for it is designed.

If you dont like it, I am sure there are other sandboxes for you to play in. No one is forcing you to participate.

Cheers,
Vandit

 

[JGobeil]

Jules,

Thanks for taking time to set this up. I think it will provide some very interesting and useful observations (the beginning point for all good science). Looking forward to participating with my Celestron 80ED refractor. I still can't achieve focus without using an extension tube, but I can include that in my summary data.

Rick Phillips
(not the same Rick)

Rick,

We have included the possibility to use spacers in the protocol if they are needed to reach focus. Please feel free to do so and mention it in the test data - there is a special line for it.

Regards
Jules

 

[Paul Corfield]

We are looking for a math formula to calculate the magnification of spacers added between the scope and the camera.

Jules

Jules,

I did some tests today to see if my Photoshop percentage method works correctly and I can pretty much say it's spot on.

I took 3 photos, one at prime focus (600mm) and then one with a 1.5X teleconverter and another with a 2X teleconverter. In photoshop I resized all three photos to 800 pixels wide. Then using the 600mm prime focus photo I resized it by 150% and then dragged it onto the photo taken with the 1.5X teleconverter. The two matched up perfectly which in theory they should have done as 1.5X is the same 150%. I repeated this with the 2X teleconverter photo by increasing the 600mm image by 200% and this matched up perfectly also. So if you take 600mm as being correct as that is the scopes focal length you should be able to multiply that by the percentage increase needed in Photoshop and then multiply by the crop factor to work out the mm equivalent. The tests I did today back that up.

Once you start stacking teleconverters then this method needs to be used. When I stacked my 2X and 1.5X you would expect the magnification to be 2880mm or 300% just by basing it on calculations alone. However when I overlaid the photos and got a perfect match it was more like 2736mm or 285%.

Paul.

 

[JGobeil]

Jules,

I did some tests today to see if my Photoshop percentage method works correctly and I can pretty much say it's spot on.

I took 3 photos, one at prime focus (600mm) and then one with a 1.5X teleconverter and another with a 2X teleconverter. In photoshop I resized all three photos to 800 pixels wide. Then using the 600mm prime focus photo I resized it by 150% and then dragged it onto the photo taken with the 1.5X teleconverter. The two matched up perfectly which in theory they should have done as 1.5X is the same 150%. I repeated this with the 2X teleconverter photo by increasing the 600mm image by 200% and this matched up perfectly also. So if you take 600mm as being correct as that is the scopes focal length you should be able to multiply that by the percentage increase needed in Photoshop and then multiply by the crop factor to work out the mm equivalent. The tests I did today back that up.

Once you start stacking teleconverters then this method needs to be used. When I stacked my 2X and 1.5X you would expect the magnification to be 2880mm or 300% just by basing it on calculations alone. However when I overlaid the photos and got a perfect match it was more like 2736mm or 285%.

Paul.

Humm... In theory, it should be x2.0 x1.5. Have you tried it stacking the other way around ? Would the thickness of the TC act as a spacer ?

Also, your scope is 600mm. Is it before or after adding the focuser which is acting as a spacer...

On another matter, I tried to find a resolution factor we could apply to compare complete setups - scope, teleconverters, barlows, spacers, DSLR. The resolution number derived from the target tells us how accurate the image is but it does not consider the distance. Obviously, a DSLR with a 50mm prime lens at 1m. will show better resolution than a DSLR/scope at 100m. What if we considered effective resolution as the resolution number on the target multiplied by the distance in meters needed to have the target full frame ?

Regards
Jules

 

[Paul Corfield]

Humm... In theory, it should be x2.0 x1.5. Have you tried it stacking the other way around ? Would the thickness of the TC act as a spacer ?

Also, your scope is 600mm. Is it before or after adding the focuser which is acting as a spacer...

Regards
Jules

I tried the converters both ways and the result was the same as in the size of the subject. Both ways it was smaller by the same amount compared to the theoretical X1.5 X2. My 1.5X converter is half the width of the 2x so if one was acting as a spacer you would have seen a difference one way or the other.

When I put the 2X teleconverter on the camera first and then stacked the 1.5X the image was slightly distorted. When I put the 1.5X on the camera first and stacked the 2X the image was perfect. This showed up when I overlayed the photo from 600mm, it was a perfect match but only at 285% so there was a 15% loss which is quite a bit (144mm). Either way I think it's a good way to work out the actual magnification rather than the theoretical magnification.

Not sure the size of the spacer attached to the scope has any relevance as all that does is determine how far the focuser is wound in or out. The distance from the objective to camera ccd remains the same when focus is reached. A smaller or larger spacer wont result in a different sized subject in the final photo.

What if we considered effective resolution as the resolution number on the target multiplied by the distance in meters needed to have the target full frame ?

Yes, this should work as an effective scoring system.

Paul.

 

[JGobeil]

Good news... I should get my scope today ! Unfortunately it's raining :C:C:C

 

[vkalia]

Good news... I should get my scope today ! Unfortunately it's raining :C:C:C

Always the case, innit? I have to wait for another 3 weeks for my toys, as I have to relocate on assignment to another country in 2 weeks. Well, lots of new birds, I guess...

V.

 

[Paul Corfield]

Hadn't planned to but I ended up testing various configurations all day today. Ended up with one that's working pretty good at all ranges up to the max I tried. Based on the way I've been working out the magnification this system is getting me to 4800mm. All info about what I used is written on the photos. First photo is at prime focus and second one at the 4800mm.

Paul.

 

[JGobeil]

Paul, how do you get the teleconverter to work with your DSLR without getting ERR 01 ?

 

[kenwin5]

I've recently started using a Nikon D80 on a Nikon ED80 Fieldscope which gives me 1500mm (as 35mm). Better results than previous P5100, and in most ways easier to use, but still mixed experiences and would like to exchange info with anyone else using same set-up.

Ken

 

[Paul Corfield]

Paul, how do you get the teleconverter to work with your DSLR without getting ERR 01 ?

Does your teleconverter have electrical contacts? If it does you may need to place a thin piece of tape across the contacts. It's common practice from what I've read from people who want to use them with manual lenses. All my teleconverters are manual so I have no contacts to worry about.

Paul.

 

[JGobeil]

Does your teleconverter have electrical contacts? If it does you may need to place a thin piece of tape across the contacts. It's common practice from what I've read from people who want to use them with manual lenses. All my teleconverters are manual so I have no contacts to worry about.

Paul.

Yes, it is a Tamron Pro 2.0X that has electrical contacts. Taping pins in not enough, the 20D has a microswitch in the mount that must be tricked in some way. The T2 adapters mounts for Canon are not exactly similar to the converter mount. 2 of the wings are shorter.

To solve the problem, I took a Kenko 12mm spacer and trimmed the wings of the mount with a Dremel. That was not enough, I also had to tape the 3 first pins of the spacer on the 20D side. No more Err 01 !

I learned about the microswitch here:
http://photo.net/canon-eos-digital-camera-forum/00KZou

Attached is the first picture taken with the scope, under rainy conditions and low light at about 75 meters. 560mm with 2.0X teleconverter and 12mm spacer for about 1800mm. ISO 1600 1/250. This is the full frame pic resized to 1024 with a little sharpening. It looks promising.

Regards
Jules

 

[Paul Corfield]

Good stuff, glad you got it working. Image looks good too. Now you just need a little toy bird like I use. :t:

Paul.

 

[JGobeil]

Good stuff, glad you got it working. Image looks good too. Now you just need a little toy bird like I use. :t:

Paul.

Yea... but we will have to start using the testing protocol. I'll try to post tomorrow

 

[Paul Corfield]

I borrowed my dads Canon 300mm lens earlier today and took a photo of my target toy Robin. Then I took one through the 600mm scope from the same position. I had to enlarge the 300mm photo by 235% to get it to match up with the 600mm one where as you would have expected it to only be 200%. Does that imply that my 600mm scope is really 705mm or that his 300mm lens is out by 35% or a bit of both? You would expect a lens to be around +/- 5% at a push I would have thought. It would seem that working out these focal lengths isn't as simple as I first thought. One way to check would be to photograph some stars and do some calculations based on known angles of separation.

Here's the two photos and you can see just visually that the 600mm one is more than twice the size.

Paul.

 

[JGobeil]

I borrowed my dads Canon 300mm lens earlier today and took a photo of my target toy Robin. Then I took one through the 600mm scope from the same position. I had to enlarge the 300mm photo by 235% to get it to match up with the 600mm one where as you would have expected it to only be 200%. Does that imply that my 600mm scope is really 705mm or that his 300mm lens is out by 35% or a bit of both? You would expect a lens to be around +/- 5% at a push I would have thought. It would seem that working out these focal lengths isn't as simple as I first thought. One way to check would be to photograph some stars and do some calculations based on known angles of separation.

Here's the two photos and you can see just visually that the 600mm one is more than twice the size.

Paul.

Interesting question Paul. Tomorrow, I will test it with my 100-400. With a 1.4 TC, it gives 560mm, similar to my scope.

 

[Paul Corfield]

I won a 2" GSO 2X ED barlow today on ebay so I'll have some fun with that when it arrives.

Paul.

 

[maxxxx]

Normally I'm not into extreme magnification (over 30x) but I thought I'd mess about with the 1000mm achro at close range just to see what it could do.

Taken with 1000mm fl achro barlowed to about 60x at about 30 feet. Almost full frame.

 

[Paul Corfield]

Normally I'm not into extreme magnification (over 30x) but I thought I'd mess about with the 1000mm achro at close range just to see what it could do.

Taken with 1000mm fl achro barlowed to about 60x at about 30 feet. Almost full frame.

How do you work out the X magnification on a digital slr. On a 35mm camera it's roughly 50mm, although I read it's nearer 44mm if such a lens was available. I read on a dslr that a 28mm lens is considered 1X.

Nice photo btw. Did you spacer the barlow away from the camera to increase the power?

Paul.