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Borg 125mm Pentax in f/6 vs. FS128 f/8.1

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#1 gnowellsct

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Posted 21 April 2013 - 08:11 PM

data on fs128

data on Borg 125 SD


I'm interested in the possibility of selling my FS128 and getting the Borg 125 SD which I took a look at NEAF.

Here are the considerations.

1. I could mount the 125SD on my C14. Currently I use a 4" on the C14. The FS128 is too big.

2. Bigger potential FOV on the 125SD vs the FS128.

3. With the Borg 125SD I might be able to use one refractor where I currently use two....

4. Portability of the Borg (weight about the same as the Vixen 4")

5. The Borg 125SD in visual configuration would apparently just be a two lenses up front without the two in back which act as a focal reducer and a field flattener for photography. So I'm wondering about the degree of color correction in the Borg vs. the longer f/8.1 FS128.

The FS128 has impressed me with its stunning low power views and its ability to hold a razor sharp image up to 300x and even higher. I don't usually use it for planets but it does happen, sometimes I go out thinking I'll be looking at open clusters and I end up looking at Jupiter or Saturn instead.

I have other telescopes. I guess mainly I would be inclined to make this change if the Borg 125 would be "as good as" the FS128 in terms of optical performance. If it were "as good as" the FS128 then the flexibility of applications would give it an advantage.

I suppose I can dip into some cash reserves and own both scopes at once to do a side by side, but it really makes sense to sell the FS128 before getting the Borg. I suppose in refractor land that makes no sense. You're always supposed to compare.

If there are people who've used both and or people who are optical mavens and know how to read the PSF tests (are there PSFs for the Borg) I should be much obliged in help with interpreting the results. What I've been able to find, I've put up.

Greg N

#2 MooEy

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Posted 21 April 2013 - 08:32 PM

You are looking at the wrong chart for the 125SD. You should be looking at the charts below instead

http://www.sciencece...125sdf39mtf.htm
http://www.sciencece...d/125f51mtf.htm

Optically it's very good, but i don't think you will find it on par with the tak. Taks are magical and in a league of their own. There's some colour, but it doesn't bother me. Vignetting is quite obvious when using the f/4 reducer, even on a small 8300 chip.

When using the 295mm tube with the drawtube removed, it fits into one of those orion backpack. This alone makes me feel that everyone should own a borg 125SD.

~MooEy~

#3 gnowellsct

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Posted 21 April 2013 - 08:39 PM

There was some discussion on astro-foren.de that the lens cell had some issues in the early versions but apparently this was corrected some time ago...

I guess part of my apprehension in changing things is that the FS128 has a rep as one of the finest visual five inch refractors ever made. I really do like mine. But I've been curious about the Borgs for some time...found a post of mine on the same topic from 2008!

#4 MooEy

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Posted 22 April 2013 - 12:20 AM

Think of it this way

It's super small and compact for a 5", behaves like a small 4" refractor but with 5" of aperture. I'm using mine on a puny manfrotto 055 tripod for those quick sessions.

Optics are very good, takes magnification well. This thing ain't going to embarrass u at any star party.

Binoviews with the shorter tube, no dumb fov robbing barlow needed. I have a pair of 14mm and a pair of 18mm radians to play with

Maintenance free, mine held collimation well. And the doublet cool down pretty fast for those quick sessions.

Modular parts, swap out the stock focuser for a nice feathertouch without spending money on custom adapters. Infact, borg's M57 system have so many adapters that you will most likely find what you need.

Nice imaging scope, I have the 7704 f/4 reducer on this, and stars are round all the way out to the edge of the st-8300m. And at f/4 this thing is really fast for those dim objects.

Optically it may not be as magical as the ap/taks, but the ap/taks can't do things that the borg can do.

~MooEy~

#5 MooEy

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Posted 22 April 2013 - 12:21 AM

For the fun of it, here's a photo of how it looks like...

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#6 MooEy

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Posted 22 April 2013 - 12:46 AM

oh ya, if u notice, the focuser on the smaller borg 71fl comes from the borg 125sd. old borg parts tend to go to newer borgs...

~MooEy~

#7 bobhen

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Posted 22 April 2013 - 09:33 AM

Greg,

Would the Tak TSA 120 work for you?

The Tak 120 OTA is 6 pounds lighter than the Tak 128 and about 4-5 pounds heavier than the Borg 125. The Tak 120 is just slightly larger than a TSA 102.

If the Tak 120 fills your weight/portability requirements it will certainly meet or surpass your optical requirements and could easily replace both of your 4 and 5-inch refractors - you won’t miss your 128!

The TSA 120 is an impressive scope both optically and ergonomically.

Bob

#8 MooEy

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Posted 22 April 2013 - 05:39 PM

A photo of the borg 125sd beside one of the smallest 4"

~MooEy~

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#9 gnowellsct

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Posted 24 April 2013 - 12:13 PM

Thank you for the answers everyone; I'm catching up on the thread. I think my NEAF itch is beginning to subside; if I sit tight, I get to keep my FS128 and I don't spend a dime. Anyway I've long thought that the real upgrade here would be to sell the 128 and get a TEC 140. I also greatly admire the Borg 5 incher's design philosophy.

I find it very difficult to go to NEAF and see all the goodies and in particular not come away all riled up about a refractor. I had made a decision to get the Pentax 125, but they weren't available yet (this was the first year they were out) immediately after NEAF, and in the calming months that came between I scored an FS128 and saved myself a bundle (relative to the Pentax 125).

I'm also thinking that $3k on a Daystar filter might be a fun way to go, keeping the current refractors. But that's a separate thought.

I really do think that if I had unlimited bucks I probably would own five or six apo refractors.... Greg N

#10 gnowellsct

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Posted 24 April 2013 - 12:14 PM

Incidentally both the FS128 and the Borg 125 are very rare on Astromart, I think only one of each in the last two years listed. The people that have them tend to keep them, it seems. Greg N

#11 jhfenimore

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Posted 24 April 2013 - 07:09 PM

Greg,

I think you should buy a Borg 125 and let me observe with it at the Landis "dark" sky site. I've been thinking about replacing my TV 102 with a Borg for the last two or three years, to get the benefits of greater aperture without a significant increase in weight. But I hear next to nothing about the scope on these threads. So I'm reluctant to take the plunge. Hope this thread brings more comments from experienced owners.

Jack

#12 gnowellsct

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Posted 24 April 2013 - 08:05 PM

Greg,

I think you should buy a Borg 125 and let me observe with it at the Landis "dark" sky site. I've been thinking about replacing my TV 102 with a Borg for the last two or three years, to get the benefits of greater aperture without a significant increase in weight. But I hear next to nothing about the scope on these threads. So I'm reluctant to take the plunge. Hope this thread brings more comments from experienced owners.

Jack


Well in visual configuration it's really a doublet and therefore not quite up to a triplet apo--from everything I've seen. The same is true of my FS128 which however is excellent and shows none of the color I've seen in achromats. But I guess folks are on about the principle of the thing. They want that triplet. Meantime I would like to know how well corrected the Borg is taken as a doublet vs. the FS128 which should be a fair comparison. And the reason it's of interest is that in visual mode the Borg is f/6 and if it really is up to the same performance level as an FS128 (or better) than it is a steal for the money.

The FS102s and 128s used to be considered the ne plus ultra of optics. You don't hear that so much any more but as I say those that gots 'em are hanging on to 'em and, as previously mentioned, same thing with the Borgs. The photographs I've seen with Borgs look excellent.

#13 MooEy

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Posted 24 April 2013 - 08:06 PM

I'm actually having thoughts about the TEC 140. I think it would be a nice compliment to my Borg 125SD. The borg is roughly 500mm f/4 in imaging mode, while the tec would give me somewhere double of that at 980mm f/7.

As nice as the FLT-98CF is, it's somewhat redundant after i got the Borg 125SD. The borg is lighter and gathers more light and goes even higher in magnification. I don't think you will use the tv 102 much after you get the borg 125.

There ain't alot of images taken with the Borg 125SD due to the lack of reducer/flattener. 7704 sold out quickly after it's being released and 7887 got discontinued. Now that both of them are back, better grab one quickly.

~MooEy~

#14 gnowellsct

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Posted 24 April 2013 - 08:07 PM

If I hit the lottery in the next year I'll get the 125 AND a Tec 140....y'all can hold me to it.

#15 gnowellsct

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Posted 24 April 2013 - 08:11 PM

I'm actually having thoughts about the TEC 140. I think it would be a nice compliment to my Borg 125SD. The borg is roughly 500mm f/4 in imaging mode, while the tec would give me somewhere double of that at 980mm f/7.

As nice as the FLT-98CF is, it's somewhat redundant after i got the Borg 125SD. The borg is lighter and gathers more light and goes even higher in magnification. I don't think you will use the tv 102 much after you get the borg 125.

There ain't alot of images taken with the Borg 125SD due to the lack of reducer/flattener. 7704 sold out quickly after it's being released and 7887 got discontinued. Now that both of them are back, better grab one quickly.

~MooEy~


Have you ever looked thorugh an FS128; and how do you think the 125SD would compare in visual mode at f/6? An FS128 will show out of focus color and I have seen FS series pics on the internet where the tendency to "blue stars" was apparent. I'm wondering how that goes with the 125 SD. Also whether you can pump it up to 300x on a steady night and have a crisp planet image.

#16 MooEy

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Posted 24 April 2013 - 08:12 PM

nono, you buy the Borg 125SD and the TEC 160/180FL.

for now, stop dreaming and buy the borg 125

~MooEy~






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