Comparing Digiscoping and Eye-piece projection (1 Viewer)

[possum]

I am not suggesting that long range digiscoping is a substitute for fieldcraft, but if you want to capture the image of a shark/whale or dolphin from land and thereby not disturb the animal's behaviour, then you have few options.

I have been using a CP 4500 coupled to a Pentax PF 100 ED scope together with a variety of eyepieces, most usually the XL21, giving x30 magnification.

Like everyone, I find the CP 4500 zoom a little soft at the far end, and so usually use it at around 2 to 3 times.

Generally I am satisfied with the results, but I get very frustrated by the camera's slow performance. In particular I am unhappy with:-

a) Slow start up speed
b) Slow continuous shooting rate
c) Huge time to write to memory after a burst
d) Shutter lag
e) Small dark LCD screen, difficult to use in very bright weather
f) Battery lifetime.

The bottom line is that I'm missing too many rare opportunities.

So when Sout Fork posted elsewhere on BF about using a Pentax DSLR body coupled to his eye-piece, like the astro guys do, I thought that I would try that route too.

After much searching and reading I decided upon a Canon 30D DSLR body because of its exceptional low noise at even 1600 ISO.

So how does it compare to Digiscoping? All the images are straight from the camera in jpeg.

The first is a picture of my 'standard' target, a sort of plywood basking shark fin. The range is 260 metres (290 yards) and this 'wide' shot was taken with a 300mm telephoto lens on the 30D - just to give you a scale.

The next photo is digiscoped with the CP4500, resized to 640x427.
The next is 100% crop from its original.

No 4 is the full eye-piece project photo just resized - note the improved colour.
The last is a 100% crop from that one's original.

The first thing to notice is that the 100% crop images have about the same pixel density.

With fewer elements in the optical train, the EP proj image is a little better.

So overall I feel that the image quality has improved a little, however I also get the extra benefits of :-

5 frames per second - just keep blasting away;
instant start up;
no delay in writing to memory;
an electronic remote that actually works beautifully;
Huge battery life - no auto focus motors to drive etc;
lots of in-camera adjustments;
can shoot RAW and jpeg simultaneously;
big LCD to view image.

The disadvantages are:-
Very heavy, very big body;
very noisy shutter as the mirror slaps up and the blind opens - it does scare the birds from the trees;
image size limited by the magnification of the EP, rather than the CP4500 zoom.

I guess you could use a zoom EP and recover that last point, but I don't have one to try.

The final bonus is that you have a DSLR to use with other lenses as well.

So as an alternative for the perfect replacement of the super CP4500, this does it for me, but it's a big heavy lump to haul around and may not suit many.

possum

 

[Sout Fork]

So when Sout Fork posted elsewhere on BF about using a Pentax DSLR body coupled to his eye-piece, like the astro guys do, I thought that I would try that route too.
possum

That's not exactly what I do. I don't use a eyepiece between the camera and the scope but rather a dedicated SLR camera adaptor. This adaptor is a high quality optical device made specifically to adapt Pentax cameras to Pentax spotters. They are not cheap however-around $400 here in the States. It turns the 100mm Pentax into a fixed aperture f12 1910mm (38x) long lens.

You can see it here:
http://www.pentax.co.jp/english/products/sougan/scope/pf-ca35/

I have used eyepiece projection on the 100mm Pentax and have found it very inferior to the dedicated camera adaptor at least with the eps that I have on hand.

All of your experience with the slowness and awkwardness of normal digiscoping methods were exactly my experience also at least with respect to in the field wildlife photography.

Here are a few highly compressed pics using this setup.

The bunny was at about 60 feet and the eagle at 1/8 of a mile and the swans about the same.

SF

 

[possum]

Stunning photos SF, can't figure if I am more impressed by the action shot of the swans or the fabulous eagle. I wish I could do as well.

I tried to buy that Pentax Adaptor in Europe, but Pentax are not at all active in wanting anyone to buy their scopes or scope attachments - you can get a quote - £335, but that's about all, no available product.

The only easy way is to buy any Pentax stuff is through the astro dealers and they stock or have access to the really wonderful Pentax fixed eyepieces and astro scopes.

For years I used to photograph clouds and sunsets with a Canon SLR fitted with a 35-85(ish) lens, coupled to the eyepiece with a bit of drain pipe. I tried 'scoping' birds with it, but it needed ISO 400 film which is SO grainy, there was absolutely no quality.

It was when I saw your original post in which you described 'Prime focus', 'Eye-piece projection' and the 'Pentax adaptor' that I got my old SLR out again.

I had never given it proper consideration until then, I sort of thought that the image would be upside down in the camera, just like in prime focus. I was just thinking ' image right way up with lens on camera, therefore image upside down if I take the lens off the camera'.

So when you posted showing the different techniques and how the image was inverted in 'prime focus' but not in eye-piece projection, I got out the camera body, fitted a T2 adaptor and started to play.

I really love these Pentax eyepieces, I use the XL series, the 21, 14 and 10.5 mm. I have a lot of other astro eyepieces, including a pair of Hyperion 21s which I often use in a bino-telescope. But the Pentax win every time especially when you start Pixel peeping, which inevitably happens when doing any very long range stuff, there just are never enough pixels.

I would like to try one of those Pentax Adaptors, the results you get are wonderful. I guess that they will have been designed for use with a flat sensor rather than a human eye with all its lens bits and curved retina. They appear to have fewer optical elements and the appropriate distance spacer incorporated to eliminate any vignetting which otherwise you get with the DSLR too close to the EP/imaging lens.

The reason I posted was to help bridge the gap in understanding on how the different techniques perform in direct comparison. I know what I get from digiscoping and so I wanted to share the comparison of one technique to the other. Sofar, with my set-up, digiscoping with a CP4500 and eye-piece projection with a DSLR give about the same quality of image using the same scope and EP.

Next step will have to be your dedicated Pentax Adaptor.

There is a KEOS adaptor that would go between the Pentax Adaptor and Canon camera. I was torn between staying with Canon and switching to Pentax, but in the end, I stuck with Canon as I have some lenses and I really wanted the 5 frames per second - dolphins are so fast and often difficult to predict their surfacing.

Also I have Hen Harriers that hunt through here all the time. I have lots of bad and out of focus shots, or infocus/half-harrier-absent shots, that I'm hoping the 5 fps will get me the shots I keep trying to achieve.

Guess maybe I should get one of those Adaptors from B&H - I have tried in the UK and Germany and failed to find anyone who could actually supply.

Anyway it was thanks to your original post that I got started down this road. Presently I feel that I can achieve as much or a little better than I did with traditional digiscoping, so maybe the next step is that adaptor of yours.
possum

 

[Sout Fork]

I had never given it proper consideration until then, I sort of thought
that the image would be upside down in the camera, just like in prime
focus. I was just thinking ' image right way up with lens on camera,
therefore image upside down if I take the lens off the camera'.

So when you posted showing the different techniques and how the image
was inverted in 'prime focus' but not in eye-piece projection, I got
out the camera body, fitted a T2 adaptor and started to play.

SF:
At prime focus (nothing between objective and focal plane of camera) and
you will get correct image because the prism in the camera will correct
for the "incorrect" image coming from the objective. The trouble comes
in when using a spotting scope with a built in prism which is already
giving you a "correct" image and then the camera prism reverses
everything once more and gives you an "incorrect" image in the
viewfinder of the camera.

So that is why the Pentax 100mm gives a incorrect image in prime focus
(with built in prism) while a astro scope in prime focus (no prism)
gives a correct image. Optically it's not as bad as it sounds because,
of course, the camera prism is not in the light path when taking a
picture. In fact all standard camera lenses are giving the camera an
incorrect image just like prime focus but the camera takes care of that
internally.

I would like to try one of those Pentax Adaptors, the results you get
are wonderful. I guess that they will have been designed for use with a
flat sensor rather than a human eye with all its lens bits and curved
retina. They appear to have fewer optical elements and the appropriate
distance spacer incorporated to eliminate any vignetting which otherwise
you get with the DSLR too close to the EP/imaging lens.

SF:
Yes. No mucking about with adaptors, spacers, swing arms, alignment nor
issues of vignetting or focus. Fast, reliable and trouble free with no
hassles out in the field.

The reason I posted was to help bridge the gap in understanding on how
the different techniques perform in direct comparison. I know what I
get from digiscoping and so I wanted to share the comparison of one
technique to the other. Sofar, with my set-up, digiscoping with a
CP4500 and eye-piece projection with a DSLR give about the same quality
of image using the same scope and EP.

SF:
That surprises me a bit. I would think getting rid of the point and
shoot camera lens would have given the edge to the SLR setup. Perhaps
both methods are so compromised that it's hard to tell the difference.

Next step will have to be your dedicated Pentax Adaptor.

There is a KEOS adaptor that would go between the Pentax Adaptor and
Canon camera. I was torn between staying with Canon and switching to
Pentax, but in the end, I stuck with Canon as I have some lenses and I
really wanted the 5 frames per second - dolphins are so fast and often
difficult to predict their surfacing.

Also I have Hen Harriers that hunt through here all the time. I have
lots of bad and out of focus shots, or infocus/half-harrier-absent
shots, that I'm hoping the 5 fps will get me the shots I keep trying to
achieve.

SF:
My Pentax camera gives me about 3fps but that is at maximum file size.
If I go down one step in files size I get about 6fps. It slows up when
the buffer becomes full so of course smaller files allows more pictures
to be stored in the camera's fast memory.

Guess maybe I should get one of those Adaptors from B&H - I have tried
in the UK and Germany and failed to find anyone who could actually
supply.

SF:
Try Here:
http://www.astronomics.com/main/pro...SEBT7C6V804B9NA99R1WMSS3L6/product_id/PF-CA35
This is where I got mine for 50 bucks less then anywhere else. Don't
know if they ship to the UK but they probibly do because they are a big
store. Make sure to click on the red "more info" part to get true price.

Anyway it was thanks to your original post that I got started down this
road. Presently I feel that I can achieve as much or a little better
than I did with traditional digiscoping, so maybe the next step is that
adaptor of yours.

possum

BTW it must be nice to be so near the sea. I'm 1200 miles from the nearest marine environment.

 

[possum]

The reason I posted was to help bridge the gap in understanding on how
the different techniques perform in direct comparison. I know what I
get from digiscoping and so I wanted to share the comparison of one
technique to the other. Sofar, with my set-up, digiscoping with a
CP4500 and eye-piece projection with a DSLR give about the same quality
of image using the same scope and EP.

SF:
That surprises me a bit. I would think getting rid of the point and
shoot camera lens would have given the edge to the SLR setup. Perhaps
both methods are so compromised that it's hard to tell the difference.


------------------
Thank you for the information SF.

This was the reason for undertaking this test, I wanted to see the contribution that the CP4500 made to reducing the image quality, and compare the two techniques.

So by keeping the same telescope and same EP and only changing the camera, it's a fairly reasonable comparison. Clearly they were taken on separate days, but overall the comparison was fair. There was reasonable light on both days and the wind had finally stopped blowing.

As I said in the first post, the quality from the DSLR is slightly better, but clearly the quality of those CP4500 optics are very good, causing only a minimal reduction of resolution/image quality.

It may be that the Pentax Adaptor produces much better images, but I was looking to assess the various contributions made to image degradation. I hope to understand the limitations of each of the components.

Take the EP for example; both 21mm Hyperions produce a significantly worse image than the 21mm Pentax and the best of the Plossl that I have (the sort $75 type) produce so much curvature to the image, that the apparent depth of focus is just a few inches.

Generally I find that the DSLR, set up as an Eye-piece projection system, is really sensitive as to depth of focus. This problem is compounded by perturbations to the air's refractive index caused by even light winds.

So an EP that gives really acceptable images when used by eye eg. the Hyperion 21s, produces really quite poor images with this EP projection technique. All of my plossls produce images which are quite awful. But with digiscoping, using the CP4500, these differences are far less marked.

I think that you have taken the right path by opting for the dedicated DSLR adaptor, and I will follow your lead.

But the point of the test was to determine that by direct comparison of an existing technique to the new one while only changing one parameter at a time. Also I am sure that there are others out there who, like me, wonder what, if any, improvement they will get by slapping a DSLR body onto their eyepiece when out in the field, rather than a compact.

I suspect that the Pentax DSLR adaptor is designed to improve the flatness of the image on the camera's sensor, as the physical sensing depth of the CMOS detector (or CCD) is much smaller that the rods and cones in our eyes, requiring a different imaging system on the telescope's output.

Thank you for the source of the Pentax Adaptor, I'll give them a try.

Yes, living by the sea is quite magical. I had 34 choughs, 2 kestrels, 4 oystercatchers, a few hooded crows, magpies, 3 curlew, some partridge, LBBs, herring gulls, this morning when I went to feed the sheep.

Some days it's basking sharks and minke whales all day, with dolphins and puffins, shearwaters and kittiwakes, we love living by the sea.

possum

 

[Sout Fork]

So an EP that gives really acceptable images when used by eye eg. the
Hyperion 21s, produces really quite poor images with this EP projection
technique.

SF:
This is just speculation on my part but I think you may have put your
finger on problem.

You are trying to compare eps designed for visual observation for their
suitability as photo lens on two very different cameras nether of which
was designed for this purpose.

At the end of the day the most one can say is that one ep+camera
combination may compromise optical performance less than another
combination but in no case does any combination work really well.

The final results would be more or less arbitrary. So much so that it
wouldn't surprise me at all that you would find a $50 no-name cheapo ep
outperforms a $400 Nagler when used this way.

It's too bad we are separated by 3000 miles of ocean. If I lived in
Liverpool I'd post you my adaptor to use for a week and you could see
for yourself if it's worth it.

As it is there are no answers, Only Choices.

SF

 

[possum]

Yes, I think you are right, I'm trying to make the EP perform in a way for which it was never optimized.

I will get the Pentax Adaptor and repeat the tests. Also that will liberate a pair Pentax XL 21s for use on the binocular telescope, where they really shine - wonderful performance.

Think I feel the urge for a 400 mm prime coming on - I need to sort out my optics for the forthcoming season. That too will be an interesting comparison, 400 prime and a 1.4TC - a bit more portable than the present set-up, less reach but should be quite effective.

Thanks for your help, I'll post some more when I get this sorted; as you say, shame the ocean is so big.
possum

 

[Sout Fork]

Just thought I'd throw this in for the heck of it...

... it's a 102mm f5 500mm fl achromatic that I got for the princely sum
of $175 delivered to my door.

I only use it for close focus photography off the porch in the Summer
and through the windows in the winter on the feeder birds.

It's setup for prime focus and gives a nice bright 15x. I use a 80mm
extension tube that moves the focus down to 9 feet.

Results?-see for yourself

 

[possum]

That looks like a great set-up SF, especially for the money. So if I understand correctly, that's an astro scope - looks like a Celestron in this case - with the Pentax DSLR operating at prime focus. So the image is the right way up when viewed through the camera's viewfinder? Produces really splendid images. Is it a bit sensitive on the focusing?

I tried the company you suggested but they don't do international sales, however I've found another that does seem to. Can you tell me what is at the camera end of the Pentax Adaptor please? Is it a T2 thread or a Pentax K mount?

One of the sites that offers the Adaptor, also offers a T2 to Canon adaptor, thereby inferring that the PF-CA35 terminates in a T2, (M42 fine) thread. If it is a T2, that would be ideal.
Many thanks
possum

 

[Sout Fork]

That looks like a great set-up SF, especially for the money. So if I understand correctly, that's an astro scope - looks like a Celestron in this case - with the Pentax DSLR operating at prime focus. So the image is the right way up when viewed through the camera's viewfinder? Produces really splendid images. Is it a bit sensitive on the focusing?

SF:
Yes correct image with a camera and no mirror/prism installed-the camera prism corrects the image. So any astro scope without a prism coupled to a SLR gives correct image. At only 15x focus in not sensitive because of good DOF.

I tried the company you suggested but they don't do international sales, however I've found another that does seem to. Can you tell me what is at the camera end of the Pentax Adaptor please? Is it a T2 thread or a Pentax K mount?

SF:
K mount only-see pic-I wonder if there is a Pentax to Canon or Pentax to T thread converter?

One of the sites that offers the Adaptor, also offers a T2 to Canon adaptor, thereby inferring that the PF-CA35 terminates in a T2, (M42 fine) thread. If it is a T2, that would be ideal.
Many thanks
possum

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