Eyepiece Projection – 2

Probably this must be 1st time for me to seriously study the astronomy mathematically.


Michael Covington’s book was the bible for astro photographer in film era. So I’m sure everyone owned that time and still handles it carefully. I looked over this time. Nothing obsolete. Still wonderful book!! A lot of scientific data indicate his great efforts. I understand collecting data that time is much harder than today.

Followings are scanned his pages.


W=(F x theta) / 206265. OK, W in mm is the image scale finally projected to the sensor. So I set “3 mm” first. Small!! Yes, small. I wish larger. But I feel this might be good number as realistic world to start studying. Theoretically 3mm diameter is 1250 pixels in ASI 183MC.

3 mm = (X x 24″) / 206265 – 24″ as Mars size at the closest.

X = 25800 mm

So my target number as the effective focal length is 25800 to achieve 3 mm as image scale for Mars. If I use 107FL= 600 mm and 150ED = 1000 mm, the required magnification is 43 and 25.8 respectively.


Then, M = (s2 – F2) / F2.

M is 43 and 25.8 in above calculation. If I use Vixen HF 2.4,

107FL : 43 = (X – 2.4) / 2.4, X = 105.6 mm

150ED : 25.8 = (X – 2.4) / 2.4, X = 64.32 mm

Most likely smaller number of F2 (closer to the sensor) should be more favor. Probably further, more blur. That’s what I guess.

Anyway, I hope this should be good numbers to start my test and practice for eyepiece projection.

I thought 2.4 mm eyepiece was too much. But now I understand not much at all. From standpoint of visual experience with BORG 107FL and Vixen 2.4, I’m expecting the good result photographically too. But I’n concern if such distance of F2 maintains good result. That’s my 1st point to see.

If I get HF 2mm, F2 will be 88 mm and 53 mm respectively.  So single HF 2 for imaging while 2 x HF 2.4 are binoscope.


150ED only displayed in showroom these years. I’ve never used more than 10 years. A bit concern about the performance. Originally it was good and I recalled it performed well in last Mars closest approach. Let me see how it will do again.

BTW, these were taken 45 years ago. OLYMPUS DIGITAL CAMERA

According to my memo,

  • Taken with Goto 80mm (F15), HM6mm and Petri V6
  • Kodak Tri-X film, processed with Fujifilm Pandol (9 minutes) and printed in Gekko V4.

Well done, Ted!! No internet and I was living in small town in Hokkaido. I’m only person who took astro picture in the town and probably even around there. Monthly magazine and technical book were my only resources. An camera shop owner only in town told I was only customer who was buying Kodak film. I believe so since Kodak film is special and so expensive (imported in 360 yen/$ era). Very poor Japan era.

Memo says the Venus taken on January 4th (and most likely 1973). It must have been really cold because of Hokkaido. So I imagined it was below zero C. I was very patient young boy that time. I’m now a spoiled California old boy and like drinking beer in the warm room inside.

And when I visited my parent house last time, accidentally I found out Takahashi eyepiece projection adapter. This original “TS” logo reminds us of the beginning time of their business. This is still good condition, well designed and made even I see today!! I try to play it around while feeling 45 years ago,  only for 0.965″ eyepiece though. My Goto scope is still in my parent house. One day I have to ship it here. Lens is useless because of mold.


~ by tedishikawa on January 29, 2018.

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