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How to understand digiscoping magnification (1 Viewer)

JLPritchard

Well-known member
OK, I am a complete newbie and I find the terminology a maze to get through. It seems some spotting scopes digiscope with only an adapter and some with an adapter and their native eyepiece. I am trying to figure out whether the lengths are always given in full format equivalence.

For example, the Kowa doesn't use an eyepiece but says the 883/884 goes from 680-1000. Does this mean I multiply by 1.5/1.6 for a APS-C and 2X for a MFT to get my magnification or lens equivalency?

The Swarovski 85mm does use the eyepiece and advertises 750-1800. Same deal - do I use a multiplier.

If this is the way it works, the Swarovski is a much more potent telephoto lens equivalent using a MFT at extreme magification over the Kowa (2000mm versus 3600mm).

Am I missing how this works? It's so hard for me to try to find the data for the various spotting scopes on how they work with adapters. Knowing that two spotters both go 25X-50X would seem to work only if I don't use an adapter with a lens but simply take a picture manually via the eyepiece.

I can't help but think I am missing some puzzle pieces. Thanks for any enlightenment.

[And I am trying to juggle this with FOV. With a wider field of view, I would think a spotter could let me go higher magnification without cutting off feed or head as a scope with narrower FOV would]
 
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You will have to multiply the figures with your camara's crop factor. I for one, use a Swarovsky ATM 80 HD, with Panasonic G3 camera (crop factor 2x) and a 30 mm lens. So at 25x magnification of the telescope, the 35 mm equivalent tele length is 30*25*2= 1500 mm. At 50x telescope magnification it is 30*50*2= 3000 mm. The camera plus it's lens can be placed behind the telescope's eyepiece with an adapter. I use a DCB adapter, but there are other adapters without a lens. Swarovsky also has the TLS-APO adapter, containing a 30 mm lens. This lens is used instaed of a normal camera lens, but the eyepiece of the telescope stays in place and so is used when digiscoping. I have no experience with other telescope brands, but I think they basically all work the same way.
 
Keep it simple stupid is the old motto and it applies here too... jan did a good job of a quick review...perfect.

Simply take your scope magnification and for digiscoping you want to be around 20-25....

In my case I have a camera which allows me up to 4 optical zoom....which is roughly 105mm....when I am in between around 3 opitical zoom I am at 85mm....

So do the math....25 scope power X either 105 or 85mm equals 2100-2600mm lens.

But honestly I prefer 20x when digiscoping.. and 3x (85mm) opitical zoom...so I usually play with 1700 zoom.....there or abouts...............

The further zoom you use the worse your images will become. So keep it simple...the least amount of zoom on your scope and the least amount of optical zoom to prevent vignetting....
 
OK, the formula is camera lens X scope mag X crop factor (1.5 or 1.7 or 2X).

So if I use my m4/3 and the APO Swarovski adapter with a 30mm lens and the scope power at 20 then I would get a lens length = 1200mm at 35mm full frame equivalence.

Now, I have read that 50mm on a full frame camera = 1 (about what our eyes see). So 2x= 100 and 3X = 150 and so on. Spotting scopes use this baseline of 50mm I understand. So a 20X Swarovski spotting scope would = 1000mm equivalent for a full frame. A 50X setting would = 2500mm. This should be the native magnification of the spotting scope without a camera, correct?

OK, lets go back to the Swaro with an APO adapter with a 30mm pancake lens. Without the camera, the spotting scope itself has the equivalence at 20X = 1000mm. With a full frame camera and a 30mm lens, the formula gives 600mm. So the camera is actually reducing the size of the image because of its 30mm lens? With a Nikon APS-C and 30mm lens, the formula gives 900mm. Still less than the spotting scope would provide with no camera, correct?

So a lens of less than 50mm reduces native magnification equivalence and a lens over 50mm enhances magnification. Have I got that right?

But then the crop factor of your camera comes into play as well other factors like vignetting if you go beyond 3-4X optical zoom or too long.

Now the Swaro keeps the eyepiece on the scope and the camera lens "looks" through the spotting scope eyepiece. Yet, the Kowa requires the removal of the eyepiece and substitutes an adapter that has a zooming function. The specs I read for the adapter on a 88mm Kowa spotting scope are:
TSN-88 Series
Focal Length: 680-1000
Magnification: 24x (approx)

This is where I get a bit lost. So if I get a Kowa and the TSN-PZ adapter and use my m4/3 camera I will get a range of magnification of only 1360-2000? Or is it saying that at 24X the range is 680-1000 depending on crop factor?

Bottom line: can I get a similar range of telephoto magnification with either the Swaro or the Kowa or does the Kowa give me a smaller range due to its adapter and no eyepiece?

Whew! Hope I haven't totally confused everyone...
 
You are right when you say that total magnification is combined tele lenght (crop factor*telescope magnification*fl of camera lens) divided by 50. So my 3000 mm 35 mm equivalent tele length will give a 5000/50 = 60x magnification. You are also right when saying that a 30 mm lens - without taking the crop factor into the account - reduces the tele length and consequently reduces the size of the image compared to the scope without the camera.

As for the Kowa: a focal length of 680-1000 is a magnification of 13.6 - 20x, not 24x. This is without the camera's crop factor, so with a micro 4/3 this has to be magnified by 2, so 1360-2000, like you already calculated. I don't know how they can argue that 680-1000 fl will give a 24 magnification.
Or is it saying that at 24X the range is 680-1000 depending on crop factor?
They can't mean that, because then the cropfactor could only be 1000/680=1.47 max. If they are right in stating that the fl of the Kowa is 1000 mm max., the Swaro will give you higher magnifications and so a larger tele length.

How much you want to magnify is a matter of taste and a matter of what you want to photograph. For relatively low magnifications the bird has to be nearby, for larger magnification the distance to the bird can be larger. I for one, don't like to sit for hours in a small tent or other hiding (except my car sometimes), so birds will be further away in most circumstances. I don't care about that. The further away the bird the less detail and if one doesn't like that, one has to get closer to the bird. I often heard and read that 24x is a kind of maximum usable or optimum magnification for digiscoping. Most of the photographs I take are at my highest magnification, so 60x, or 3000 mm tele length. Under good circumstances it is possible to take good photographs (but less detailed) at that magnification, at least to my standards. If you are interested you might take a look here http://janvangastel.nl/ and judge for yourself. Your mileage may vary, of course.
 
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This is how I have understood things. There's a huge difference between using the scope as a prime lens, which requires an adapter that moves the focal point from hidden inside the scope to behind the adapter, enabling the real image to be projected onto the image sensor or film plane.
Typically, these adapters convert a spotting scope with 480 to 500 mm focal length to an 800 mm f/13.3 lens. Numbers may vary, but these are typical.

Now, if we have a full-frame camera body, the focal length will be 800 mm, which corresponds to 16x magnification if the 50 mm lens is considered "normal".
(800:50 = 16).
But if the crop factor is 1.5x, the magnification will be 24x (16x1.5) which corresponds to a 1200 mm lens at full-frame. 1.5x800 = 1200.
And with a M4/3 body, it will be like using a 1600 mm lens with full frame.
The real focal length is still 800 mm, though.

The other kind of digiscoping is totally different. By photographing the virtual image as seen through the eyepiece, we achieve vastly better better brightness and often more magnification.
Independent of whether we use a P&S camera with 8 mm as "normal" lens or a full-frame body with a 50 mm lens, we have a certain image scale and angular image width that is similar to the human eye's.
If we mount any camera with a "normal" lens behind a scope with a certain magnification, we will have the very same linear magnification in the images.
The concept of "crop factor" is not to be used when digiscoping through the eyepiece.
But the magnification can be compared to a telephoto lens by multiplying the magnification with 50, e.g. 1500 mm for a 30x eyepiece.

If the camera behind the eyepiece doesn't allow the use of a "normal lens focal length", which is common with zoom P&S cameras, they may be used at the wide end.
If we for example get the least vignetting at a wide angle setting that correspond to a 30 mm lens with full-frame, the primary image scale is 30:50 = 0.6x.
If so, the calculated focal length of 1500 mm from the above-mentioned example must be corrected with a factor of 0.6x. 0.6x1500 = 900 mm.

Then again, some cropping is usually done, and the crop will in turn increase the "imaginary" focal length.


Conclusion:
Don't confuse the use of a prime lens or a spotting scope with a photo adapter with digiscoping through the eyepiece.
In the first case, crop factors may be used to calculate the corresponding focal length.
In the second case, the imaginary focal length is calculated by multiplying the magnification with 50 and with the primary image scale through the camera's lens if it's not a "normal lens".

//L
 
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The concept of "crop factor" is not to be used when digiscoping through the eyepiece.
Yes, it is to be used behind the eyepiece as well. The actual magnification is - assuming a 2x crop factor - twice that of a full frame camera (crop factor =1). The focal length is the fl of the lens times the magnification of the scope and the f/value is this calculated fl divided by the telescope's aperture. So the crop factor is not relevant for that. But it is relevant to calculate the total magnification and the equivalent 35 mm tele length.
 
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Just one thing that got a bit lost in this discussion. The Kowa 883/884 can also be used for digiscoping, that is using a mechanical adapter (without any lens) to couple a digital camera to one of its regular eyepieces and the camera photographs the image formed by the eyepiece. There are such adapters made by Kowa itself as well as independent manufacturers and some people even make their own. Thus if one uses a 25x eyepiece on one of these Kowa scopes, a DSLR with a crop factor of 1.5 and a 50mm lens coupled to the scope's eyepiece then the effective SLR focal length of the combo will be 1.5 x 50mm x 25 = 1875mm. Notice that 1.5 x 50mm =75mm is just the effective SLR focal length for 50mm lens on a DSLR with a 1.5 crop factor.
 
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Yes, it is to be used behind the eyepiece as well. The actual magnification is - assuming a 2x crop factor - twice that of a full frame camera (crop factor =1). The focal length is the fl of the lens times the magnification of the scope and the f/value is this calculated fl divided by the telescope's aperture. So the crop factor is not relevant for that. But it is relevant to calculate the total magnification and the equivalent 35 mm tele length.

I have a very hard time trying to understand what you're saying.
To calculate the 35 mm equivalent focal length you simply take the scope's magnification and multiply it by 50.
Then, if it's not a normal lens you use, you have to adjust the result by how the lens you use relates to a normal lens for the format you're using.
For example, if the normal lens is 25 mm and you're using a 15 mm wide angle behind a 30x scope, the formula for calculating the 35 mm equivalent will be
(30*50)*(15:25) = 900 mm.

For me, crop factor relates to the image scale when the image is magnified (view on a screen or printed) to the same outer dimensions.
A photo from a small sensor must be magnified more to have the same outer dimensions as as photo taken with a larger sensor.

What you actually mean with "actual magnification" escapes me totally, because a lens with a certain focal length projects a real image on the sensor, and that image has a constant size that follows with the focal length.
That is for me the real magnification (the size of the real image projected onto the sensor). Once viewed on a screen or a print, it has another size.

//L
 

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Let's talk specific rather than general. I think I understand the Swaro ATX/STX method for figuring telephoto equivalence.

Focusing only on the Kowa 88mm prominar and the TSN-PZ camera adapter and my Olympus PEN Mini E-PM2 which is a 2X crop camera: what would my expectations be for zoom range? Anyone actually use the TSN=PZ adapter? I am suppose to remove the eyepiece and the camera lens so neither figure into the equation. The adapter itself has a zoom function.

I am adrift on trying to understand, with this specific setup, what my shortest and longest equivalence would be.

Thanks!
 
Pretty simple really. In this configuration, the 88x w/PZ adapter combo provides a zoom range of fl=680mm-1000mm/F7.7-11.4. This is the standard true focal length format used all 35mm SLR camera lenses.

But your Oly's sensor has a 2x crop factor so the angle of view of this lens is equivalent to fl=1360mm-2000mm/F7.7-11.4

In contrast, the Swaro ATX w/TSO APO will give much longer equivalent focal lengths BUT at the cost of aperture "speed", i.e. ~F8-F22 on the ATX95

The problem you will have is that m4/3 sensors already start to suffer diffraction effects at apertures as small as F8, so image sharpness starts to suffer from the get go at any focal length.
 
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Pretty simple really. In this configuration, the 88x w/PZ adapter combo provides a zoom range of fl=680mm-1000mm/F7.7-11.4. This is the standard true focal length format used all 35mm SLR camera lenses.

But your Oly's sensor has a 2x crop factor so the angle of view of this lens is equivalent to fl=1360mm-2000mm/F7.7-11.4

Thanks! That seems to be exactly correct. I just now found a website explaining it as you have:
http://www.kowaproducts.com/kowa-digiscoping-adapters/KowaTSNPZf680-1000mm/

That's a bit disappointing to me. It's a rather narrow range for a zoom.
 
For a variety of technical reasons, you will find the ideal digiscoping effective focal length range to be 1500mm-2700mm. Anything less and you are better off with a traditional lens like the Sigma 50-500. Anything more, and shutter speed gets so slow and ISO gets so high you have a hard time with consistent IQ.
 
I know I am being a pest but...

The Swarovski APO adapter has a 30mm pancake lens, no camera lens and the 25-60X eyepiece for the 85mm scope and 30-70X for the 95mm scope. So the specs are predictably:
Focal Length 750 - 1800 mm (with 65mm or 85mm scope);
900 - 2100 mm (with 95mm scope)

This fits the formula fine.

That would give me either the equivalence of 1500-3600 or 1800-4200 with my Olympus camera.

That means I would have a dramatically higher range for the Swarovski that the Kowa.
So my final (I hope) question, is the Kowa fine for most digiscoping situations or would I regret not having the higher power of the Swaro?

[RJM - I was typing my post as you posted. So it sounds like maybe I should bite the bullet and go for the more expensive Swaro to get over 2000mm equivalence...]
 
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The PRIMARY advantage of the Swaro TSO APO is that you can change between visual scope/digiscoping lens rather quickly while with the Kowa PZ it is not really practical.

If your primary reason to buy either of these is for digiscoping then you are better off going with the Kowa Lens Scope solution, http://kowa-prominar.com/product/telephotolens/index.html

However, even this has been somewhat superceded now IMO with the ease of use of the Nikon One system using the FT adapter and 80-400 lens
 
I do envision this as primarily a digiscoping venture. But the Kowa lens system would cost me more than a Swaro and only give me fixed lenses at 1000 and 1700mm. I like the idea of framing with a zoom.

I have never previously heard of the Nikon One system with FT adapter as a digiscoping solution. Would you multiply the lens by 2.7X and then another 2X for the camera? Do you get autofocusing?
 
Go back and read my edit of post #13.

IMO, if your goal is to take HIGH QUALITY images for print you really do not get much practical advantage with the extra focal length the Swaro TSO APO offers other than record shot. Understand you will be shooting with small apertures or F14+ when you exceed an effective (including 2x crop) fl=2400+ on the ATX85. Well into the Oly's sensor diffraction limited territory.

Actually, I think because the TSO APO lens is rather generic, it also imparts some chromatic aberration even at lower powers.

As for the Nikon ONE system, yes you can get AF and VR with the right lens. Very cost effective, hand held solution.
 
So, if I used an APS-C camera with lower crop factor would that improve aperture size and picture quality? For example, if I substituted an EOS SL1 over an MFT. Or would that be irrelevant to the aperture "speed"?

I could also simply bypass the Kowa PZ adapter, go to a DA10 adapter, and get a 3X lens of low F number?

My head hurts and I am going to bed!

Really appreciate your sharing your expertise with me. Thanks!
 
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