Jump to content

Banner.jpg.692da9ed9af2eace53e1dc94cfc0e912.jpg

34mm - 82 degree EP - does one exist?


AstroJOE
 Share

Recommended Posts

I'm trying to get the widest FOV I can out of my CPC 1100. It has a FL of 2800mm and I want a medium to low power EP that is going to give me some decent wide angle views. I'm also going to be purchasing a 2" diagonal in the very near future to help with this. Currently I'm only able to get about 0.6 degrees.

I figure a 34mm 82 deg EP might be what I'm looking for? Afterall 2800mm / 34mm = 82.3mm..... 80 deg / 82.3mm = 0.99 AFOV right?

Are my calculations correct or am I approaching this from entirely the wrong angle (ahem)?

Any advice on achieving my goal with this scope would be welcome!

James

Link to comment
Share on other sites

If you have a 2" EP, the maximum field stop is going to be 46-47mm. Using 46mm we get

maximum true FOV = arcsin(46/2800) = 0.94 deg. This would require a magnification of 77.2x to be accommodated in an 82 deg AFOV (assuming no distortion), and thus a 36mm. I have not seen these. The best you can do is get a Vixen LVW42mm (47mm field stop), Panoptic 41mm (46mm field stop), TMB Paragon 40mm (45.6mm field stop) or SW Aero 40mm (Paragon clone). I actually sold my Paragon 40mm after I noticed I was not since it after the arrival of the 31T5 Nagler. The difference in TFOV was too small.

  • Like 1
Link to comment
Share on other sites

Wow indeed. See it next to the 82 degree version for scale...

asae%2520es%252030%2520100%25202.jpg

Edit: I am thinking about buying one for my 7" triplet but I want to hear how it performs first. David Nagler has said that controlling all the aberrations in an EP becomes incredibly difficult with EPs larger than 2".

Edited by DirkSteele
  • Like 2
Link to comment
Share on other sites

A 38mm SWA might suit as an inexpensive option for this low focal ratio. Better, at mid price and light weight, competing with the SW Aero is the 36mm Baader Hyperion Aspheric with an AFOV of 72* and a field stop of 44mm (my measurement), which I can recommend.

  • Like 2
Link to comment
Share on other sites

I looked through the Baader aspheric 36mm in the 16" RC of our university (F/8) and compared it to my 40mm TMB Paragon. Very similar in performance. I thought the TMB Paragon had a slight edge over the Hyperion, but that might be me being chauvinistic about my own EP :rolleyes:

At F/10 various SWA alternatives like the Panaview 38 and the WO 40 could work very well indeed.

Link to comment
Share on other sites

A 38mm SWA might suit as an inexpensive option for this low focal ratio. Better, at mid price and light weight, competing with the SW Aero is the 36mm Baader Hyperion Aspheric with an AFOV of 72* and a field stop of 44mm (my measurement), which I can recommend.

this

Link to comment
Share on other sites

Wow indeed. See it next to the 82 degree version for scale...

asae%2520es%252030%2520100%25202.jpg

Edit: I am thinking about buying one for my 7" triplet but I want to hear how it performs first. David Nagler has said that controlling all the aberrations in an EP becomes incredibly difficult with EPs larger than 2".

I use one on my 80/480 triplet for close up work, balance is tricky but it really is very good on newspapers
Link to comment
Share on other sites

There are two way to approach this task, the direct one is buy a 40mm 68 degree eyepiece or the 41mm Panoptic, in any case something in that neck of the woods. This used with the diagonal will give you your maximum FOV as Michael states a little under 1 degree, I have the same issues with my LX 12 inch. There is also another way where you can get more, this is by using a focal reducer and a two inch diagonal with no more than a 28mm eyepiece. Now here you can use either a 28mm SWA by either Meade or ExSc, both will give you a touch more Field of View. I do however intend trying , but have not tested, the same F6.3 reducer with a 26mm Nagler, this will give you over 1 degree. in yours it would be about 1.1 degrees. At the moment I do not know if this will vignette, though I think not. I any case the 28mm SWA will work and I have used this many times. The downside of these larger eyepieces is the weight and I found that a balance system was a must but the 40mm Aero is much lighter and will also give you good results. Hope this is of some use, Alan.

  • Like 1
Link to comment
Share on other sites

When after the widest view I could get with my C11 Opticstar suggested their Ascension 38mm SWA with a 70 deg fov. Probably not the best available ep but I am happy with it and it only costs £65. In fact I probably use it more often than my 23mm Axiom. If my maths is correct it gives a tfov of 0.95 deg.

  • Like 1
Link to comment
Share on other sites

I do not think that this 3 inch eyepiece which will require a different and heavier diagonal will be a viable option on the type of scopes we are talking about here. In my opinion the 41mm Panoptic ( and similar eyepieces ) and standard 2 inch diagonal should not really be used on the back of scopes like CPC 11 and LX, 90 and 200 for extended time periods without some sort of counterweight

I believe a balance system is a must for this, bear in mind the scope could also have a Crayford on the back as well. I would not like to think what my scope would look like fitted with the 3 inch system and enough counter-weights, if it were I don't believe it would do much to increase it's working life. I also doubt that the scope would ever see the Zenith, though without balance that may be all it ever does see.

Alan.

Link to comment
Share on other sites

I use one on my 80/480 triplet for close up work, balance is tricky but it really is very good on newspapers

Is the focuser strong enough to support your scope? I assume you put tube rings on the eyepiece barrel and attach the eyepiece to the mount, then you mount your scope on the eyepiece, right? :D

Edited by E621Keith
Link to comment
Share on other sites

OT but how's the big apo breaking in? I read you were due to take delivery a few months ago but I must have missed the first light thread if you posted one. Actually hope to see one on the scope forum if you have the time. Cheers.

Wow indeed. See it next to the 82 degree version for scale...

asae%2520es%252030%2520100%25202.jpg

Edit: I am thinking about buying one for my 7" triplet but I want to hear how it performs first. David Nagler has said that controlling all the aberrations in an EP becomes incredibly difficult with EPs larger than 2".

Link to comment
Share on other sites

  • 2 weeks later...

OT but how's the big apo breaking in? I read you were due to take delivery a few months ago but I must have missed the first light thread if you posted one. Actually hope to see one on the scope forum if you have the time. Cheers.

It was actually delayed thanks to LZOS in Russia receiving an order for "Space Optics" from the Russian Space Agency which bumped the production of my lens. I am not due to take delivery in the next couple of weeks. Hopefully plenty of threads to come on the new scope over the coming months.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.