Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

  • Announcements

    sgl_imaging_challenge_banner_solar.jpg

     

N3ptune

Question for - Skywatcher 200p F5 owners

Recommended Posts

N3ptune    831

Hello owners of 200p, I would be interested to know what is the longest focal length EP this telescope can tolerate before you get problems seeing the central obstruction and maybe the focuser tube.

Right now with a 32mm FL, 40mm field stop EP, I don't see the central obstruction while observing at night, at least now when my eye is placed at the exit pupil disk, no problems.  I would be looking at the ES 34mm 68d maybe, if anyone tried 34mm FL or even more with the 200p, I would be interested to know where is the breaking point.

:icon_biggrin:

Thanks

Share this post


Link to post
Share on other sites
Charic    1,942

If you take your entry pupil (mm) for your eye and multiply by the focal ratio of the scope and stay inside that ball park figure, then you should not see the central obstruction.
How much further you go will be trial and error, as each pair of eyes will reach the point you desire differently!
Refractor users  don't have the same limitations when they want to go low power .

Edited by Charic
  • Like 2

Share this post


Link to post
Share on other sites
triton1    581

I did at one time have a 40mm plossl 1 1/4 fitting and had no problem at all except I found the magnification too low so I went to a Es Maxvision 28mm in a two inch fitting for low power viewing,I would expect the 34 to perform very well.

  • Like 1

Share this post


Link to post
Share on other sites
N3ptune    831
1 hour ago, Charic said:

If you take your entry pupil (mm) for your eye and multiply by the focal ratio of the scope and stay inside that ball park figure, then you should not see the central obstruction.
How much further you go will be trial and error, as each pair of eyes will reach the point you desire differently!
Refractor users  don't have the same limitations when they want to go low power .

Ok, well following this procedure, and using a diameter of 6mm for my pupil x 5 I get 30 maximum, I use 32 with no problems now. So I guess 34 is a bit over even if the exit pupil is 6.8, which should also be a bit over my maximum entry pupil. that's good to know.

1 hour ago, triton1 said:

I did at one time have a 40mm plossl 1 1/4 fitting and had no problem at all except I found the magnification too low so I went to a Es Maxvision 28mm in a two inch fitting for low power viewing,I would expect the 34 to perform very well.

Ok that's making me more happy :p

Share this post


Link to post
Share on other sites
N3ptune    831

I finally managed to DO IT! and now we all know about my entry pupil, there are no more secrets.

I took a picture of my pupil in the dark with the flash, after almost 15 flash in my eye, SUCCESS. And I would say the results are GREAT!! If it's not 7mm it's very close (((: yeah yeah yeah :icon_biggrin::hello2:

:icon_queen:

Test was done in a dark room, the camera was in front of me on a coffee can at the right height with 10 seconds retarder time, automatic mode with macro , flash on and a precise ruler. This is so nice.

cTLUHfQ.jpg

Edited by N3ptune
  • Like 2

Share this post


Link to post
Share on other sites
F15Rules    1,602

That is fascinating!

It suggests you are quite a young person to achieve such a large EP?

I don't know what mine is but at 61 I'm sure it isn't anything like that, sadly😕.

I have owned the ES34 68 by the way, and it's a lovely eyepiece..I now have the 28mm 68 (Maxvision version) which is also a large EP, and also delivers great views😁.

Dave

  • Like 1

Share this post


Link to post
Share on other sites
N3ptune    831
4 hours ago, David Levi said:

Hi @N3ptune. Great photo! You may have started a new craze on this forum: 'Show us your entry pupil' :icon_biggrin:

hahahah Yes possible! (:

 

5 hours ago, F15Rules said:

That is fascinating!

It suggests you are quite a young person to achieve such a large EP?

I don't know what mine is but at 61 I'm sure it isn't anything like that, sadly😕.

I have owned the ES34 68 by the way, and it's a lovely eyepiece..I now have the 28mm 68 (Maxvision version) which is also a large EP, and also delivers great views😁.

Dave

I am 36 now with a bit of luck it seems! Maybe yours is not bad either! It could better then you think.

Everyone should do the measuring exercise like David Levi suggests!

Edited by N3ptune
  • Like 2

Share this post


Link to post
Share on other sites
Charic    1,942

N3ptune.....They have great difficulty in photographing my eye?  even with dilation drops, my eye is shut before the shutter! a little frustrating when they need to take 4 -5 shots per eye,  to get one that's useable.
One consolation though, I'm really seeing Stars when I leave, after all those flashes!! 

I asked the professionals that assessed my son's eyes prior to LASIK  treatment and they assessed an average pupil of 4.9mm under the test condition, so that puts me around the 30mm mark too (29.4). I have no issues using my two inch  32mm Panaview, and the verdict prior to purchasing was that the 32mm would probably be better than the 38mm?

Not sure I need to go any longer with my focal length, the Moon looks pretty small in the 32mm with its 70°afov, but as it is, the panaview is good enough for viewing M31 and general wide field viewing, when inside my Dob tent, when I don't have access to the normal finderscope in that situation?

  • Like 1
  • Haha 1

Share this post


Link to post
Share on other sites
Louis D    657

The only time you'll experience the issue of seeing the secondary shadow with eyepieces that result in large exit pupils is during the daytime when your entry pupil drastically contracts.  Bird watching and solar observing would be two instances of this.  It can get so bad you have to move you eye to the side a bit to look "around" the secondary obstruction.

Share this post


Link to post
Share on other sites
N3ptune    831
4 hours ago, Charic said:

N3ptune.....They have great difficulty in photographing my eye?  even with dilation drops, my eye is shut before the shutter! a little frustrating when they need to take 4 -5 shots per eye,  to get one that's useable.
One consolation though, I'm really seeing Stars when I leave, after all those flashes!! 

I asked the professionals that assessed my son's eyes prior to LASIK  treatment and they assessed an average pupil of 4.9mm under the test condition, so that puts me around the 30mm mark too (29.4). I have no issues using my two inch  32mm Panaview, and the verdict prior to purchasing was that the 32mm would probably be better than the 38mm?

Not sure I need to go any longer with my focal length, the Moon looks pretty small in the 32mm with its 70°afov, but as it is, the panaview is good enough for viewing M31 and general wide field viewing, when inside my Dob tent, when I don't have access to the normal finderscope in that situation?

30 to 32 mm would be ideal for me too (38 is too much) but following a study I did in my previous post to replace my Q70 wide field EP, It seems like the 34mm corresponds the best to what I want at the end of the day.  I wanted the maximum possible TFOV with at least 68-70d AFOV, 30mm FL minimum, some good corrected optics and an eyepiece that is not taking the place of my 25mm Xcel LX.

I like to look at the dense star fields and large open clusters very much, general wide field viewing is major.

Has a matter, I ordered the 34mm this morning from Explore Scientific USA, I am now the owner of a superior quality wide field eyepiece  :icon_biggrin: 

2 hours ago, Louis D said:

The only time you'll experience the issue of seeing the secondary shadow with eyepieces that result in large exit pupils is during the daytime when your entry pupil drastically contracts.  Bird watching and solar observing would be two instances of this.  It can get so bad you have to move you eye to the side a bit to look "around" the secondary obstruction.

I noticed that with my 32mm during the day, but it's still usable on the sun.  I don't use wide field 32mm during the day to watch the sun, it's not not much of an issue.. it's more 18mm, 7mm, 4.7mm usually and I also see the obstruction within these.

(; and i am the owner of a 34mm now

 

Edited by N3ptune

Share this post


Link to post
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

  • Recently Browsing   0 members

    No registered users viewing this page.

×