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Best eyepiece for the MM4 50ED - the SDL or HDF? (1 Viewer)
- Thread starter b-lilja
- Start date
pete_gamby
Birds? What Birds?!
SDL is brighter and sharper and has the added benefit of being fully waterproof. Table below shows FOV for current and previous generation SDL compared to HDF.
HTH
Cheers, Pete
HTH
Cheers, Pete
| Mag | FOV deg | m@1000m | ||
| 41270 SDLv3 | min. | 12 | 3.3 | 56.7 |
| max. | 36 | 2.1 | 37.2 | |
| 40936 SDLv2 | min. | 12 | 3.0 | 51.5 |
| max. | 36 | 1.9 | 33.3 | |
| 40862 HDF T | min. | 12 | 3.2 | 56.4 |
| max. | 36 | 1.5 | 25.5 |
Hi,
I don't think so, but you don't need it... you need to know two formulas and the data above plus the given magnifications for some Opticron body with one of the EPs listed above from the Opticron page - or the body focal length:
magnification = body focal length / eyepiece focal length
SDLv2 and 3 as well as the HDF-T are all 8-24mm zoom EPs. So we get a body focal length of 288mm for the MM4-50 (12*24 = 8*36 = 288).
For my Kowa TSN-3 with its 420mm focal length that means that I get 17.5-52.5x magnification.
apparent field of view (in deg) = true field of view (in deg) * magnification
This is formula is a bit of an approximation and does ignore eyepiece distortion, but for calculating the field for the same EP on a different body it's going to be fine.
So for my TSN-3 with the SDLv2 we first calculate the afov of the SDLv2 at the low and high mag end - 36 deg at the low mag end (12*3) and 68.4 deg at the high mag end (36*1.9).
We then devide these two values by the magnifications at their respective end of the zoom range and get 2.1 deg at 17.5x and 1.3 deg at 52.5x for the TSN-3.
And if you want to convert a true field value in deg to the more common notation in m at 1000m distance, you can just multiply by 17.45m (or multiply the tfov in deg by 52.5 ft for the true field in ft at 1000y).
Joachim
I don't think so, but you don't need it... you need to know two formulas and the data above plus the given magnifications for some Opticron body with one of the EPs listed above from the Opticron page - or the body focal length:
magnification = body focal length / eyepiece focal length
SDLv2 and 3 as well as the HDF-T are all 8-24mm zoom EPs. So we get a body focal length of 288mm for the MM4-50 (12*24 = 8*36 = 288).
For my Kowa TSN-3 with its 420mm focal length that means that I get 17.5-52.5x magnification.
apparent field of view (in deg) = true field of view (in deg) * magnification
This is formula is a bit of an approximation and does ignore eyepiece distortion, but for calculating the field for the same EP on a different body it's going to be fine.
So for my TSN-3 with the SDLv2 we first calculate the afov of the SDLv2 at the low and high mag end - 36 deg at the low mag end (12*3) and 68.4 deg at the high mag end (36*1.9).
We then devide these two values by the magnifications at their respective end of the zoom range and get 2.1 deg at 17.5x and 1.3 deg at 52.5x for the TSN-3.
And if you want to convert a true field value in deg to the more common notation in m at 1000m distance, you can just multiply by 17.45m (or multiply the tfov in deg by 52.5 ft for the true field in ft at 1000y).
Joachim
Hi Jaochim,
Thanks for this post. Is there any way to calculate the aFOV or m at 1000m for the middle part of the zoom range for these scopes? I.e., calculate the FOV for the MM4/SDL v3 at 25x, or the FOV for the TSN 883 at 45X? This would allow a more apples to apples comparison of different scopes at the same magnification. Thanks.
Hi,
unfortunately not, one could of course assume that the afov is just linear over the zoom range, but it really isn't. See the below link for data on some real world example:
www.cloudynights.com
Joachim
unfortunately not, one could of course assume that the afov is just linear over the zoom range, but it really isn't. See the below link for data on some real world example:
New Baader Mark IV 8-24mm Zoom Eyepiece - Eyepieces - Cloudy Nights
Page 1 of 20 - New Baader Mark IV 8-24mm Zoom Eyepiece - posted in Eyepieces: Ive just taken delivery of a Baader Mark-IV 8-24mm Eyepiece. I finally decided to get one after having an 8-24mm Celestron Zoom and really learning to appreciate the ability to instantly fine-tune magnification for...
Joachim
Thank youHi,
unfortunately not, one could of course assume that the afov is just linear over the zoom range, but it really isn't. See the below link for data on some real world example:
New Baader Mark IV 8-24mm Zoom Eyepiece - Eyepieces - Cloudy Nights
Page 1 of 20 - New Baader Mark IV 8-24mm Zoom Eyepiece - posted in Eyepieces: Ive just taken delivery of a Baader Mark-IV 8-24mm Eyepiece. I finally decided to get one after having an 8-24mm Celestron Zoom and really learning to appreciate the ability to instantly fine-tune magnification for...
Joachim
Thanks Jring...yes I can do the maths, but I was expecting the manufacturer to make the specs available to customers who are considering upgrading (who are actually part of the market they would go an buy the eyepiece). They are very basics specs the ones being asked at the end of the day...
Ratal
Well-known member
MM4 50 ED and SDL V2 user here and I couldn't be happier. Ultra light, massively portable and I rave about this crazy good set up. *
* And I found the portability to be a thing of great beauty when I found myself knee deep in the Arctic Norwegian snow or shifting desert sands of North Africa.
* And I found the portability to be a thing of great beauty when I found myself knee deep in the Arctic Norwegian snow or shifting desert sands of North Africa.
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