Revelation Photo-Visual Eyepiece kit

[NickW]

How do people rate the Revelation Photo-Visual Eyepiece kit.... It seems like good value to me as a newbie which is rather important atm given I just spent all my money on the scope and mount.

Currently all I have is the stock 28mm 2" EP that came with my SkyMax 150 scope.

Would I be better buying one other lens to start with that's of better quality and maybe a Barlow? I did also wonder about the Hyperion zoom... but have read mixed things about that.

Oh and ultimately I would love to take some pic's which most likely will have some bearing on the choice made..

As ever many thanks for your thoughts and collective wisdom

Nick

[E621Keith]

Hyperion zoom is very good optically, and I don't think anyone doubt that. The problem is in their zoom mechanism. Probably best to look for a older Mk2 version rather than the current Mk3.

The Revelation eyepiece kit has some fairly good plossl, but I'd opt for a few BST explorer instead.

Most people image by connecting camera directly to the scope and image at prime focus. Your eyepiece selection has no effect on imaging because the eyepiece isn't used (unless you do eyepiece projection with a phone or point and shoot camera).

[mallorcasaint]

I have the Revelation set and the eyepieces are excellent for the price. You also get a set of filters and a barlow. For a beginner or if you are going to be mostly doing imaging it's a great set of EP's.

[NickW]

Thanks.

BTW: As I have a 2" diagonal is it preferable that I use 2" eyepieces where possible or doesn't it make any difference... the scope comes with a 1.25" adapter.. just wondering is optically there's a preference?

[E621Keith]

There are no difference between 1.25" and 2" eyepiece except for wide angle. The only advantage of 2" eyepiece is that they allow field stop diameter larger than 1.25" which in turn allow larger true field. As such it only benefits wide field eyepieces design.

What is the baffle tube diameter on the Skymax 150? My C6 has a 1.25" baffle tube, so I won't gain anything thing by using 2" apart from improve mechanical strength from the 2" fittings. I suspect the SM150 may have the same limitation.

[NickW]

Hi Keith...

By baffle do you mean the corner bit in the diagonal? From memory the whole diagonal is large so i am assuming its 2". I will check tonight.

when you say "they allow field stop diameter larger than 1.25" which in turn allow larger true field."... do you mean that you can get a bigger field of view things without using one of those reducers I have seen advertised? (Sorry I am a real newbie and and still finding my way round this new language)

Nick

[E621Keith]

The baffle tube in a SCT or MCT is the tube going through the middle of the primary mirror, its internal diameter will limit the field. It is the diameter of the opening in the back of the scope. This limits widest view possible with the scope. The diagonal doesn't matter because the field (image) will be cropped before it leaves the back of the telescope and only the cropped image will reaches the diagonal and eyepiece.

A reducer will indeed increase the field of view by shrinking the image scale, but only IF the field was not limited by the baffle tube. The maximum true field visible in an eyepiece is limited by the eyepiece field stop diameter, that is essentially the diameter of the optical window at the telescope side of the eyepiece. A larger field stop diameter will allow you to see more true field. It's a bit like a DSLR sensor. e.g. when you have a 50mm lens, a 35mm FX sensor will see the lens as a 50mm, while a smaller DX sensor will see a cropped image at the centre that's 1.6x smaller than FX. An even smaller 4/3 sensor will see only half as much field as the FX sensor. The lens hasn't change, but the smaller sensor will see a smaller field because of the crop. The same applies to eyepiece field stop, 1.25" eyepiece format is a bit like a 4/3 camera, the camera is physically too small to fit a FX sensor inside. If you want to see the full 35mm FX's field using a FX sensor you'll need a bigger camera housing, and this is where the 2" eyepiece format comes in.

A reducer is a bit like a device that will convert your dx sensor into a FX equivalent. However, if you use a DX lens on a FX camera, you will see black image frame with a circular image in the middle. This is because the DX lens cannot produce a image wide enough to cover the FX sensor. This is similar to the C6 with a 1.25" baffle. Whether this will affect the SM150 will depend on its baffle diameter.

I hope this make sense.

[NickW]

Keith

Thanks for that extensive and patient answer I really appreciate you taking the time to explain it to me.

I just did some quick reading around and it seems the SM150 has a 25mm baffle which means it will have a limited FOV but I couldn't find anything official quoting it. It makes me wonder why a larger diagonal is put on then.

Nick

[E621Keith]

A large 2" diagonal have mechanical advantage over 1.25" diagonal. This can be important when you use heavy accessories. I use 2" visual back and diagonal in my C6 because I use heavy zoom eyepiece and the 2" connection have a better grip.