4mm Ortho

[Littleguy80]

1 minute ago, Dave1 said:

Very interesting Neil. 

As you push the magnification up the exit pupil gets smaller and therefore the image should get dimmer. The fact you say it seemed brightest with the 4mm Ortho is very interesting indeed. You must have a great 4mm eyepiece there! Hang on to that one.

I've just purchased a 7mm Fujiyama orthoscopic eyepiece, to add to my collection! To fill a gap for viewing the planets. Should work well with my 80mm telescope and 102mm telescope!

Thanks Dave. It could be a perception thing as the background will also get darker with the smaller exit pupil. It’s a great little eyepiece though. I’ve read lots of good reports on the Fujiyama orthos so I don’t think you’ll be disappointed!

[John]

On 03/05/2018 at 09:48, Littleguy80 said:

More fun with the 4mm Ortho last night. M57 was the target. Located with the 9mm Lunt and then worked my way through my Ortho collection. 7mm Meade RG, 5 and 6mm BGO and finishing with 4mm Circle T. All of the Orthos showed the mag 13 star next to the ring with averted vision. It seemed brightest with the 4mm to me but still required averted vision. This felt like a good test run for Neptune and Trition later on in the year. A couple of weeks back, I had a look at M57 through an 18" dob and the mag 13 star was easily held in direct vision with that. No central star though. I also tried all the Orthos on Albireo last night for fun. I can confirm it's still one of the prettiest doubles no matter what the magnification is!

Interesting report Neil.

I use the stars around M57 as my limiting magnitude guide when the object is more or less overhead. The faintest I've done is magnitude 14.7 with my 12" dob and that was using very high magnifications - 350x - 400x but in my case with the TV Nagler 2-4mm zoom. My 4mm HD ortho does not seem to go any fainter and the central star of M57 has, so far, proved just a touch beyond this scope from my back yard observing site. The nebula itself seems better observed (more structure and contrast) at slightly lower magnifications bit it is still fun to watch it creep into view and fill much of the field at 500x or so

Here are my target stars (arrowed ones I've "got"):

 

[Littleguy80]

20 minutes ago, John said:

Interesting report Neil.

I use the stars around M57 as my limiting magnitude guide when the object is more or less overhead. The faintest I've done is magnitude 14.7 with my 12" dob and that was using very high magnifications - 350x - 400x but in my case with the TV Nagler 2-4mm zoom. My 4mm HD ortho does not seem to go any fainter and the central star of M57 has, so far, proved just a touch beyond this scope from my back yard observing site. The nebula itself seems better observed (more structure and contrast) at slightly lower magnifications bit it is still fun to watch it creep into view and fill much of the field at 500x or so

Here are my target stars (arrowed ones I've "got"):

 

Wow! Very impressive, John! That's a great diagram, thanks for sharing! I'll have to have another play and see if I can get any others. I should try from my local dark site to see if that gets me any other stars