A Digiscoping Dilemma

My present ‘standard’ digiscoping set up with the Leica apo-Televid 77 is: a B32 WW eyepiece on the scope and a Digilux 1-Televid adapter connected via a 49-46 stepping ring to a Panasonic Lumix LX5 camera. To fill the frame and minimise vignetting with this set-up the camera has to be on maximum zoom (19 mm). This gives me a 35 mm full-frame camera equivalent focal length of 2675 mm. I use an attachment made by Richard Franiec that fits into accessory shoe of the camera and allows a standard cable release to be used to press the shutter button.

Panasonic Lumix LX5 with Digilux 1 adapter
stepping ring attached to 32 WW eyepiece on
apo-Televid 77

However, the LX5, introduced in 2010, does not take full HD video and the whole set-up with so many glass surfaces is inclined to flare. Travelling abroad means having to carry another camera, charger and the Digilux/stepping ring adapter. For most distant shots my superzoom Nikon bridge camera (1000 mm full-frame equivalent) is fine. It is only for the really distant shots that the digiscope offers an advantage.

I have been trying the Phone Skope system for digiscoping with my iPhone 6 to see if that would be a better bet for carrying when travelling. The dedicated phone case (only just available in UK from Newpro) and special adapter for the Leica 32 WW eyepiece work very well. The video from the iPhone 6 with its Sony sensor is of high quality and, of course, full HD. The disadvantage of the set-up is the maximum effective focal length that can be obtained: 960 mm and effectively the same as my Nikon superzoom camera. (For incorporating stills into full HD video, I do of course, have the option of only using 1920 x 1080 of 3264 x 2448 pixels of the i-Phone image, thereby gaining extra magnification by what is a ‘digital zoom’.) However, I can see occasions where I shall use the Phone Skope set-up. If the scope and tripod are locked on a bird then it is a matter of moments to attach the Phone Skope, and start the video or take a still using a remote release or the volume control on the ear-phones.

iPhone 6 in Phone Skope case and adapter for 32 WW eyepiece

Without my Lumix LX5 set-up I would lose the capability to go beyond 1000 mm full-frame equivalent focal length. Should I get a new superzoom camera with an even greater maximum focal length which could take raw stills and full HD video, and ditch the LX5 and Digilux adapter, its lack of hull HD now being a major disadvantage? The gain in optical quality and greater depth-of-field might offset that loss of focal length that my present digiscoping set-up can achieve. For travelling abroad that might be the best bet, with the iPhone (which goes abroad with me anyway) and very light Phone Skope to latch onto the Televid if necessary.

Decisions have to me made…

Digiscope or Superzoom Bridge Camera for Birding?

A correspondent who sells secondhand optical equipment for birding on eBay tells me that the prices of digiscoping adapters for major brand telescopes are falling. He thinks the rise of the Superzoom ‘Bridge’ cameras I have discussed in this blog is the reason. The extra focal length gained by using a scope (see my Post of 19 August 2012) is now of marginal advantage when we can get the 35 mm equivalent of 1200 mm focal length from a superzoom. Add the large number of pixels captured and the fact that there is image stabilisation in the superzoom, then I can see why the digiscoping may become a thing of the past fairly quickly.

It is obviously much quicker to point a superzoom camera at a bird than it is to mount the scope on a tripod, aim and focus the scope, attach the camera by whatever attachment you have and then press the shutter.

Another correspondent says he has just had a rare bird accepted from a photograph at 1000 mm equivalent with his Nikon P510 handheld.

Over the next few weeks I will eventually get round to comparing my two systems (Nikon P50 Superzoom vs Leica Televid and Panasonic Lumix on adapter) side by side at the mouth of the river and in the garden.

Focal length of digiscopes compared to camera lenses

Does that mean you don’t have to fiddle about putting a camera on the telescope, then?

That was the question asked when I was showing off the capabilities of the Nikon P510 at the 35 mm camera equivalent of 1000mm. The question was also loaded in that it implied I would not need to buy a camera for digiscoping to replace the old Canon Ixus that fitted the scope awkwardly. The follow-up question — Surely that 1000 mm lens is as good as a scope isn’t it? — sent me in search of data. Evidence that useful as the 1000 mm is, it could not match the focal lengths of a telescope plus camera was needed. What is the focal length of a digiscope set-up in terms equivalent to a 35 mm full-frame camera?

I thought I could remember that the formula was the focal length of the camera lens multiplied by telescope magnification (with the focal length of the camera lens expressed in 35 mm full-frame camera equivalents). Sure enough, that is the formula given on the Swarovski website:

To determine the equivalent focal length for a digital camera compared to a 35 mm camera, you need to carry out a few calculations. Each digital camera has a 35 mm equivalent figure. For the Nikon P-6000, for example, the 35 mm equivalent figure is 28–112 mm. Since the Nikon P-6000 has a digital focal length of 6–24 mm, this results in a factor of 4.66 (28 mm divided by 6 mm). This factor or the 35mm equivalent focal length is usually stated in the camera’s user manual.
In this case, the equivalent focal length is the adjusted focal length of the digital camera multiplied by the factor 4.66. Example: The Nikon P-6000 is set to a focal length of 14 mm. 14 mm x 4.66 = 65.2 mm focal length equivalent for a 35 mm camera.
To obtain the entire 35 mm equivalent focal length from your digiscoping equipment, you need to multiply that focal length by the magnification of your scope.
Example: Your telescope is set at 20x magnification. 65.2 mm x 20 = 1,304 mm total 35 mm equivalent focal length
To determine the total digital focal length of your digiscoping equipment, you simply need to multiply the focal length of your digital camera by the magnification settings of your telescope.
Example: Your digital camera is set to 14 mm focal length; the telescope is at 20x magnification: 14 mm x 20 = 280 mm total digital focal length

           http://www.swarovskioptik.com/en/digiscoping_faqs

So I thought I would try it out in practice, because as, we shall see below, this is not the only formula doing the rounds on the internet. The old Ixus is ‘on loan’ and I had to use the only camera in the house that was vaguely suitable — my wife’s underwater Panasonic Lumix DMC-FT3 with its square lens housing. I managed to hold this to the eyepiece and zoom in until there was a full frame without vignetting. I then looked at the metadata. The camera focal length was 7 mm. The factor needed to convert to 35 mm equivalent was calculated from the actual zoom range of 4.9-22.8 mm and the stated 35 mm equivalent of 28-128 mm. 28/4.9 is 5.71 and 128/22.8 is 5.61 so I took the mean of 5.66. The telescope magnification was 40. Therefore, the 35 mm equivalent focal length of the whole set-up was 5.66 x 7 x 40 = 1584 mm.

The story does not end there because the Google search showed other sites which showed calculations for focal length. In the first (http://www.birddigiscoper.com/2009/08/digiscoping-math.html), I could not see how the writer had derived the formula or the constants used. Putting the same values into his formula I came up with a focal length of 2263 mm! Another website (http://www.digibird.com/primerdir/primer0.htm) provides an Excel spreadsheet which came up with 1720 mm. In the latter case, the difference is in the way the 35 mm equivalent focal length of the camera lens is calculated but since I do not know how a constant used for the calculation was derived I cannot comment further.  These cases demonstrate how dangerous the internet is for spreading and retaining incorrect information. I have shown the web addresses but not shown them as links for this reason.

Just in case you are wondering whether Swarovski got it wrong and the other guy is right (even though I could find no basis for the formula he came up with), I did stand in the same place with my Nikon P510 and take a picture at 1000 mm equivalent of the same object at the bottom of the garden. I then measured the size of the object in relation to the width of the frame on the screen. In my crude Lumix digiscoped shot, the object occupied 0.58 of the total width; in the Nikon it occupied 0.36 of the width. Dividing one by the other, 0.58/0.36 = 1.61. Thus, the focal length of the digiscope was 1.61 times that of the Nikon or 1610 mm, remarkably close to the calculated 1584 mm given the crudity of the size measurements. Clearly, the formula given by Swarovski is the one to use when calculating the focal length of a digiscope set-up when using a digital compact camera. I just hope that people find that one first in any Google search.

The focal length of any digiscope set-up can be calculated from the camera focal length (found in the metadata after taking), the manufacturer’s stated zoom range in 35 mm equivalents and the magnification of the telescope eyepiece.

And, just in case you were wondering, great as the 1000 mm equivalent lens of the Nikon P510 is for birds, it does not replace the digiscope entirely. Much longer focal lengths can be achieved with the latter but whether there is enough light or time to set up the scope is another matter.

Eyepieces of course

The original version of the previous post refered to 'objectives' instead of 'eyepieces' Thanks to a contributor to Birdforum for pointing out the obvious error. I have only two excuses: 1. I had been working on a consultancy project involving different microscope objectives and must have had objectives on the brain when I was writing about eyepieces for telescopes; 2. Is age catching up with me?  The post, including the diagram, has now been corrected.

Which Eyepiece for Leica apo-Televid 77?

I carry three eyepieces with me when using the apo-Televid 77. Why?

Over the years we have had the opportunity of testing all the eyepieces made for the 77/62 range side by side and under different lighting conditions. The eyepiece lenses (available only on the secondhand market) are:

20x WW (41009)
32x WW (41011)
40x (41003)
40x WW (41007)
30-60x Zoom (41005)

Let’s start by considering the zoom.

The 20-60x zoom eyepiece (41005) is one I do not use. It has an angle of view of 1.9-1.2˚ equating to a 34-20 metre field of view at 1000 metres. At 20x magnification, its exit pupil is 3.85 mm (making it brighter, on paper, than the 20x WW) decreasing to 1.28 at 60x. There are several reasons why I do not favour this eyepiece. It has a narrow field of view compared to the WW series. It is pretty useless at magnifications above 40x under normal lighting conditions and it lacks the clarity and brightness of the single magnification eyepieces, despite the relatively large exit pupil. Having a family with two apo-Televid 77s, an apo-Televid 82 and an apo-Televid 62, the general comment is that Leica did not get the zoom right until the 82.

The other eyepiece we do not use is the 40x (41003) — the early, non-wide variety. It has a relatively narrow angle of view (1.25°; 22 metres field at 1000 metres) and a small exit pupil of 1.25 mm. The WW version is far superior.

In terms of Field of View the WW lenses are far superior as the diagram below shows.

Now to the eyepieces I carry with me:

I usually have the 40x WW (41007) fitted. It has a 1.8° angle of view (32 metres field at 1000 metres) and an exit pupil of 1.8 mm. It is a superb lens. But if the light is relatively low or a wider field is needed, then I can quickly switch to the 32x WW (41011) (2.3° angle of view — 40 metres field at 1000 metres; 2.3 mm exit pupil). Another superb lens. If the light really starts to fade or if I want to scan and count then the 20x WW (41009) comes into its own. This gives a 3.45° angle of view (60 metre field at 1000 metres) with an exit pupil of 3.45 mm.

40x WW fitted on the Apo-Televid 77

The value of carrying three eyepieces was illustrated by an evening in the Eric Morecambe  Hide at the RSPB’s Leighton Moss reserve. A flock of Black-tailed Godwits looked superb with the 40x WW but as the light began to fade, the 32x WW was needed. As the colours began to become indistinct, a quick change to the 20x WW brought the scene back to life.

The three WW eyepieces I carry

A factor in choosing eyepieces is digiscoping. It is worth noting that the Leica Digital Adapter 2 (42303) nor the Digilux 1 Adapter (42302) will not fit either of the 40x eyepieces. The diameter of the various eyepieces for fitting digiscoping collars are: 54 mm (32x WW); 53 mm (20x WW and 20-60x); 50 mm (40x WW); 45 mm (40x). It is worth talking to SRB Griturn about digiscoping adapters for all these eyepieces.

SRB Griturn can be found at: http://www.srb-griturn.com

Leica Digital Adapter 2 (42303) fitted to 32x WW eyepiece

Finally, these eyepieces were also made for the Televid 62 but have lower magnifications (by a factor 0f 0.8). 40x becomes 32x, and 32x becomes 26x on the Televid 62.