Apeture and Focal Length

I'm not sure if this is the best forum for this question, but after reviewing all the forums twice, it looks like it fits here. Anyway, here it goes . . .

Apeture and Focal Length. It seems I'm striving for both. I live in a very light polluted area. Each year, it seems to grow worse. In 2-3 yrs. I will remedy that by buying a new house a bit more in the country. Until then . . . For now, I'm battling with this issue. What is the biggest and easiest, etc.

It seems I'm settling into the 3000 mm F/L. I really like the sounds of two scopes.

1. Tak Mewlon 250. 3000 mm F/L.
2. TEC MC200. 3150 mm F/L.

I'm very interested in the TEC because it is lighter, easier to handle, has a tad bit more F/L, but 2" smaller apeture. It is also $1,200.00 cheaper. Minus a couple of necessities.

Is apeture in this quality of scope going to make up for the 150mm less of F/L, or will F/L make up substancially for the difference.

My knowledge of scopes is rather limited, although I have had two CAT's, two very small MAK's and two APO refractors.

Any input would be appreciated,

Steve

Well, it depends on what you want to do with it. The FL is only critical for prime focus photography (in which case you usually want it to be shorter, since you can always make it longer with a barlow or eyepiece projection). Other than that, you can get the same magnification just by using different eyepieces. And a 150mm difference out of 3000+ really isn't going to make much difference. So a scope with a 2000mm FL using a 20mm eyepiece gives the same 100x that a 3000mm FL scope gives with a 30mm eyepiece.

Focal length does not add resolution. APerture does, and adds light gathering as well. I am not sure what you think the FL gains you except about 5% more mag with the same eyepiece (but the Tak will be able to reach both slightly wider max TFOV and noticeably higher max mag than the TEC).

What exactly do you want the scopes for? Are you planning to do photography? Or is it mainly visual use? Portability is an issue with any scope, unless you have an observatory for it, but I am not sure what benefit you will get from the longer FL.

Jarad

These scopes are almost identical in terms of focal length, one is just 5% 'longer' than the other. You will not see any material difference in terms of magnification with a given eyepiece, eye relief, etc.

However, there is a 25% aperture difference, which will show a material difference in performance. The 250mm will win this hands-down.

But if convenience is an issue none of this matters. An 8" scope getting used is better than a 10" sitting in the closet. At what point that trade-off becomes the decision point is a personal issue.

Thanks Jared, Paul and Bill,

I have a new G-11 that I thoroughly love. So the scopes that I have used and plan on using will be used on this mount. A new dovetail is always available for almost any scope.

Since my last two scopes were Tak refractors, an FS102 and then 128, I have developed a taste and eye for very fine optics.

I'm on the list for an AP 5", but still have about a 4 year wait. I wish to also adquire a premium CAT or MAK. I love the idea of the Mak because they come very well collimated whereas the CAT needs tweeking, and I would like to avoid that process. Maybe I am just being wimpy about it, but I like to pull my scope out, knowing that I am getting the best possible view without having to tweek collimation, or wonder if collimation is off, or is it just bad skies. And here in Northern, KY we only get about 110 Clear nights and I have not figured out the percentage of really good seeing.

Also portability is a factor, since for now, I remove the OTA from my mount and take the G-11 out in two pieces.

I would love to go for the TEC 10", but that quickly becomes a small forture, more than $2,000.00 over the Tak Mewlon 250.

Oh well, these are just a few of thoughts that I keep kicking around.

Thanks,

Steve