Posts Made By: Doug Bell

Hi All,

It seems that a lot of us talk about small refractors without realizing that the different size scopes fall into quite different classes. This image is for everyone who's wondered if a 100mm scope was enough, without having had the chance to look at one.

The scopes are:
A "Serious Size" 130mm f6
A "Travel Size" 94mm f7
The ubiquitous ST80 80mm f5

I tended to lump them all into the "small refractor" group and was quite surprised by the size difference. Are you?

Clear skies,
Doug Bell

Hi All,

Well, I thought the big & fast refractor topic merited its very own thread.

A few weeks ago I had the chance to compare a 160mm f7 and a 130mm f6 APO under very dark skies and found a few surprises. It looks like people might be interested in what I found, or at least we could compare notes.

The short story is that the 130 is the instrument of choice for wide field views. Here's why:

1) It has a wider field. I was using a 31 Nagler for just about as big a field as is possible in these scopes. The 130 provided about 3.3 degrees, the 160 just over 2 degrees. It doesn't seem like much difference, but it is and it surprised me. The wider field really opens up. Wide objects like the veil and the North American were well framed, star hopping was easier, and the Scutum star cloud was just astounding.

2) The 130 is easier to handle. The 160 is a good 50% bigger, heavier, and scarier. I breathed a sigh of relief every time I got the 160 into its case. It is as much as I'm comfortable lifting onto a mount. The 160 also put you in some awkward positions when viewing close to the zenith.

3) The 130 puts less demands on the mount. I used a losmandy G-11 for both and wouldn't hesitate to recommend it to anyone for visual use. However, where the 130 is over-mounted, the 160 maxes out the G-11. We had some breezes and a 15 mph wind restricted the 160 to about 70x. The 130 could handle the same breeze to about 150x.

4) The 130 was just as bright. The 31 Nagler on the 130 delivered a 5mm
exit pupil which is a good match for my 48 year old eyes. The 160 delivered more light, but at a magnification that resulted in a 4mm exit pupil. It slightly "over-magnified" the images and resulted in a slightly dimmer view for wide field.

Bear in mind that this is strictly a wide angle comparision. The 160 was clearly superior on faint objects such as galaxies, or anything magnified over about 40x. The seeing didn't support any comparsion on planets, although I know that the 130 can give excellent planetary views.

The truth is that I can't say that an achromat wouldn't do just as well at the low powers I was using. But I am pretty sure that an achro couldn't do the wide field and the planetary the way the apo does; and it's easier for me to rationalize one apo than the two achros I'd need to get both views.

The conclusion is that I don't see any benefit for going over about 130mm for a wide field scope. As always, your mileage may vary.

Thanks,
Doug

Hi Maurice,

A product matching this description is "EZ Strip" which I bought from Randy Cunningham at Astro Systems. I've watched it being used, and have a can, but haven't used it myself. I try to avoid lens cleaning whenever possible.

The other similar item you'll hear about is collodion. I can verify that it works great on lenses, but I abandoned it and don't recommend it. I never felt safe working with it as it's exceptionally volatile and can be explosive.

If I had such a lens I think I'd be looking for professional cleaning / alignment. Perhaps D&G or one of the other lensmakers would take it on.

Good luck,
Doug

Hi Eddie,

It can get miserably hot. Expect daytime highs in the 90's. Those nice sunny days we want can get into the 100's. If you're camping you'll want some shade and plenty of water.

It's not darker than TSP or the American Southwest, but it is as dark. The sky darkness is limited only by the natural skyglow. That's the natural limit and is the same issue for TSP, or for that matter, the middle of the Indian ocean. And you do notice. The sky takes on a magical quality that is missing even at the relatively dark sites around my home in SE Nebraska. There are a variety of phenomena that I've only seen at NSP.

Clear skies,
Doug Bell

Hi Robert,

I know several people who transport big dobs in trailers. For big scopes (18+ inches) I don't see many alternatives. It seems to work quite well but you need to take precautions to make sure everything is well secured. Trailers bounce and vibrate.

A big plus for a trailer is that they provide on-site storage at a star party. It's quite reassuring when you see those thunderstorms rolling in. Some people are also able to store they scope in the trailer full time. It saves a lot of packing/unpacking before a trip.

Best wishes,
Doug Bell