Baader Morpheus 6.5mm vs Vixen SLV 6.0mm

[Ricochet]

3 hours ago, Shooting star said:

So you are in essence saying remove the 28mm piece and re evaluating that, it makes sense as still a pretty even spread of magnification. 

Actually, I was saying to keep the 28mm but not to worry about barlowing it. I was assuming that you would be looking at something like an ES68° which is a 2" eyepiece rather than 1.25".

3 hours ago, Shooting star said:

What has thrown me is what you say about barlowing the 38mm piece will require 2" barlow. Presumably, that is because that specific focal length does not come in 1.25" did size? I can't find a 1.25" eyepiece focal length chart, but by looking at a number of brands it would appear that physics is dictating 2" pieces at this long focal length.

The barrel size determines the maximum true field of view (tfov), which is the amount of sky you can see. This translates to the following limits:

• 50° - 32mm
• 68° - 24mm
• 82° - 18mm

If you want a longer focal length then either you have to move to a 2" barrel or you have to restrict the apparent field of view (afov). A 38mm 1.25" format eyepiece is going to limit the afov to somewhere around the 40° mark. To me this feels too restrictive and I would not use such an eyepiece. If you want to stick to only 1.25" eyepieces then I would suggest you look for a 24mm 68° eyepiece (ES68°/Maxvision/Meade SWA) as your longest focal length. However, I have found that a slightly bigger tfov is preferable for framing certain objects which will dictate at least one 2" eyepiece.

[Louis D]

1. Don't bother trying to barlow long focal length eyepieces.  You'll get vignetting and/or edge of field cutoff and finicky exit pupils that are difficult to hold.  It can be done with a telecentric barlow like the TV Powermate or ES focal extender, but those cost a lot more than a similar barlow.
2. I would keep the 38mm in your list for lowest power viewing and for centering objects for higher powered viewing.  I would skip past the 28mm and head right to the 15mm to 22mm range for the next power.  The 9mm and 12mm choices are good, though if you have a 15mm to 18mm mid-power eyepiece, the 12mm will feel redundant.  I would go for a 5mm to 6.5mm eyepiece for high power views.
3. So, to summarize, 38mm, 16mm, 9mm, and 5mm eyepieces.  You won't have much need for a barlow with that spread.  You can jostle the focal lengths up or down a bit and still be in great shape.  For example, I use 40mm, 17mm, 10mm, and 5mm eyepieces the most in my 8" Dob.