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Towa 80 dimmer than Tasco / Sears 76

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#1 Jae

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Posted 19 September 2006 - 07:04 PM

It started when I compared a mint Towa 80 with a mint but older Tasco 10TE. To my surprise, the Towa's image was dimmer than the Tasco. How could this be ? 4mm more and the lens seemed even cleaner than the Tasco. :confused:

:foreheadslap:
I decided that the light was being blocked by various baffles.

So following Keith's advice - if it ain't broke, take it apart to find out why.......first step was to remove 2 baffles in the focuser which seemed very narrow and constricting. The result showed very slight improvement in brightness.

This was eating at me. I noticed similar brightness issues with 60mm Towa/Sears versus a 60mm Tasco.

The only baffle left was the one in the main tube, I figured it needed to move a few inches towards the focuser. Well I didn't have the patience to think it through and decided to take a baseball bat and tap it back. I placed some cardboard circles to cushion the blow.

Finally ! I checked the two scopes......Towa 80 is slightly BRIGHTER than the Tasco.....mission accomplished. No cosmetic damage outside, a little touch up inside maybe needed. The image is very contrasty, sharp and it may very well be superior to the Tasco 10TE, perhaps owing to the 4mm advantage.

So much for that... :)
Jae

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#2 trainsktg

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Posted 19 September 2006 - 07:18 PM

In this case, the bigger hammer trick actually worked! Well done.

:smash:

Keith

#3 dfell

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Posted 20 September 2006 - 10:18 AM

It would be interesting to emeulate TeleVue and remove all baffles and flock the interior to see if it improved the scope further.

#4 Jae

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Posted 20 September 2006 - 05:10 PM

I partially got this effect by flocking the focuser tube but I didn't have enough for the OTA so I put the baffle back in after knocking it out completely. Took a pair of pliers and bent the tabs to get more friction. But sounds like a great project......in the end, even a classic telescope has to perform to it's full potential. If I didn't have other 3"ers laying around, I might have never noticed but the DIFFERENCE IS DRAMATIC. I'd say about like the XLT / UHTC / BB coating effects used in newer CATS.

#5 Awesomelenny

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Posted 20 September 2006 - 07:41 PM

HI Jae,

This was a very interesting thread to read. Actually , you would be able to tell exactly if the baffle was interfering by simply moving the star focus way out until you just see a large disk which would be just an image of your objective. You should also have been able to just make out the little spacers between the two lens elements. Have you ever tried that? Try that with let's say a 9mm or thereabouts eyepiece and a nice bright star like Vega as your illuminator.

I have also read somewhere by someone who realized that somethimes if you have too long of a focuser drawttube and if it's inserted to far in the focuser, the front end of the drawtube acts as a baffle and cuts off the edge of your objective too!

#6 krehmkej

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Posted 20 September 2006 - 08:21 PM

Hmmm, Interesting. I have the same TOWA sitting on my shelf. Have been considering unscrewing the entire focuser/drawtube, machining an adapter and extending the tube to accomodate a 1.25 inch focuser. I have always suspected there was a lot of vignetting going on in there.

#7 Jae

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Posted 21 September 2006 - 07:27 AM

Hi Lenny,

I'll have to try that this weekend with a star to see what you mean. I kind of get it but not sure.

On the focuser, I try to remember to rack it all the way out then use the drawtube to get to focus and pull it a bit more out and then use the rack to back into focus for just the reason you mentioned.

This Towa might outperform the Unitron 3 incher......we'll have to see. :grin:

#8 Awesomelenny

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Posted 21 September 2006 - 09:20 AM

You know, if you find that to be true, I could strongly recommend that you buy another aluminum tube with the extra length needed. I could recommend a supplier that sells custom sizes of aluminum, brass, and stainless tubes. I needed a odd tube for the solar screens of my 4 inch Unitron and they had some really nice stainless steel tubes cut to exactly what length I needed and boy does that ever look good now.

Then what you could do is mount the lens cell by means of stainless allen set screws into threaded holes (by you) in the aluminum tube. Then you could purchase a nice Moonlite refractor focuser with just 4 inches of travel. Now think of THAT as one awesome refractor!

WOW! :woot: :woot: :woot: :woot: :woot: :woot: :woot:

#9 droid

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Posted 21 September 2006 - 01:37 PM

I noticed similar brightness issues with 60mm Towa/Sears versus a 60mm Tasco.





Jae; not any more, thanks for the Meade lens , its still a tad dimmer but I think thats to be expected allowing for the focal length differances.But it out contrasts all my 60mms now, want it back?????? hmmmmmmm

#10 Jae

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Posted 21 September 2006 - 04:22 PM


I noticed similar brightness issues with 60mm Towa/Sears versus a 60mm Tasco.


Jae; not any more, thanks for the Meade lens , its still a tad dimmer but I think thats to be expected allowing for the focal length differances.But it out contrasts all my 60mms now, want it back?????? hmmmmmmm


Good deal, Andy! Nah, I enjoy you making good use out of it. That Meade lens was hand picked out of 5 by Bill Vorce. How about posting some moon photos ?? :grin: Wonder if banging out the baffles would still be better...... :question: Could follow Lenny's advice to check..

#11 droid

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Posted 21 September 2006 - 06:13 PM

Got a baseball bat I cna borrow???? :p

#12 refractory

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Posted 22 September 2006 - 10:18 AM

How about the other way round- what if I hollow out a baseball bat and insert my optics? The f ratio will be relatively short, and I'll need to think about stops. Short. Stops. Hmmmmmmm.....

Jess Tauber

#13 droid

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Posted 22 September 2006 - 10:23 AM

that might work , if..................., you can figure out whos on first base....... :shrug:

#14 dfell

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Posted 22 September 2006 - 10:34 AM

I found that with the Towa original eyepieces, there was no vignetting but using a .965/1.25 adapter with plossls 25mm and longer there was significant vignetting because the long focus tube had to be further in and the .965 barrel size cut the usable aperture noticably. The choice to be made is do you leave a classic telescope stock and have it keep it's value or do you modify it for modern eyepieces to enhance it's use as an observing instrument. I decided not to modify the instrument and use an apo instead and just use the scope with it's original eyepieces, etc. once in a while as reminder that in it's day this scope was state of the art and to remind me how far amateur instruments have come and what we take for granted nowadays.

#15 Jae

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Posted 22 September 2006 - 12:54 PM

I found that with the Towa original eyepieces, there was no vignetting but using a .965/1.25 adapter with plossls 25mm and longer there was significant vignetting because the long focus tube had to be further in and the .965 barrel size cut the usable aperture noticably. The choice to be made is do you leave a classic telescope stock and have it keep it's value or do you modify it for modern eyepieces to enhance it's use as an observing instrument. I decided not to modify the instrument and use an apo instead and just use the scope with it's original eyepieces, etc. once in a while as reminder that in it's day this scope was state of the art and to remind me how far amateur instruments have come and what we take for granted nowadays.


That makes good sense - to keep the classic for use with the original .965 eyepieces, but I have an interesting dilemma. Now what would you do if your scope is an Orion branded Towa that came with a hybrid diagonal and 2 - Orion 1.25 inch eyepieces ? :question:

Right off the bat, if I use a .965 to 1.25 adapter and use a 1.25 diagonal, I get improvement with stock eyepiece.

#16 Darenwh

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Posted 22 September 2006 - 01:11 PM

I think I would start by seeing if the focuser tube of the scope actually needs to be as long as it is. If you can focus all the origional eyepecies and still have a couple inches of outward travel then maybe it would be possible to shorten the tube, keeping the classic looks, and elliminating the vignetting on the 1.25" eyepeices.

#17 droid

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Posted 22 September 2006 - 08:18 PM

That makes good sense - to keep the classic for use with the original .965 eyepieces, but I have an interesting dilemma. Now what would you do if your scope is an Orion branded Towa that came with a hybrid diagonal and 2 - Orion 1.25 inch eyepieces ?

Right off the bat, if I use a .965 to 1.25 adapter and use a 1.25 diagonal, I get improvement with stock eyepiece.






Jae; send em to me, Ill send you the .965 diagonal and .965 eps :rofl5: :rofl5:

#18 dfell

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Posted 23 September 2006 - 10:35 AM

I have to agree that if you want maximum observational usefullness, you would have to retube and add a new focuser, the only thing you would keep would be the objective and cell. probably best to go with a 2" focuser. That depends on whether the lens is good enough to justify the modifications.

#19 Darenwh

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Posted 23 September 2006 - 02:09 PM

Of course, if the cell is one that is screwed to the main tube, you could try to find the same size tube, get it machined to accept the same cell, and then set it up with the new focuser. result: Can just move cell back to origional tube to get it back to the classic.


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