addition to my TV 102 for planetary

[Bender]

I am trolling for some inputs for a potential addition to my TV102 for planetary. I am generally quite satisfied but have sometimes a natural craving to be able to increase magnification.

I feel that i am most of the times stuck with my TV 8mm (110x, ep 0.9) plossl as the best magnification before the image starts to blur and becomes unstable on Jupiter and moon.

My theory is that a bigger apperture should give me higher mags for an ep of 1mm and hopefully enable me to push the magnification to say 150-180 before the image gest blurry.

I am a strickt visual observer with alt az mounts and dont have to much space at home, limitting the options somewhat plus with certain limits on my available time a 2h cooldown for a big Mak Cas would not be ideal either. I was thinking a 8" f6 newt on my AyoDigi mount or a C8 might be nice but i read different views on what improvements i can expect.

[earth titan]

Improved image stability on planets is more than just aperture, although it does play a major part. Combining aperture and focal length for planets is the real game changer.

In my pursuit for a good planetary scope, that doesn't take up too much space, I ended up with an SCT. I know your concerns re cool down but they and MAKS really are the best for planets for those with restricted space, due to their longer focal lengths. My C9.25 works well upto 8mm (TV plossl) in terms of magnification before I get the image blurring. This would make it about x290, purely due to the focal length of the scope (2350mm) and the increased aperture. Not bad for my town centre location.

[ronin]

Something sounds wrong, I would have expected a TV102 to get 150x easily, from what I can read it is a 102mm f/8.6 Apo. It really sounds like one of the scopes that could get 200x as in twice the diameter.

Do you know anyone with a 5mm BST ?

If so drop that in and see what transpires, but I assume by 8mm TV you mean the TV plossl, again they are very good. So you appear to have a very good scope and a very good eyepiece. So I am more then a little puzzled.

Have you manage to do anything to it like drop out of a third floor window, or cleaned the lens cell in a dish washer. :eek:

What were the conditions when planet viewing?

Maybe the sky was poor, will ask if you have used it several times or just one or two, and the normal time viewing occurred, and if the latter then maybe you have been unlucky and had poor conditions.

As mentioned I would have expected that scope to deliver 150x without any trouble at all.

[ChrisLX200]

The smaller aperture scope, especially a refractor, will perform better (inch for inch) in mediocre seeing than a larger aperture scope. However, for resolving power you need the larger aperture. If you want higher magnification then a x5 TV Powermate will get you there with standard eyepieces and avoids the extremely short f/l required using eyepiece alone. Works on my Genesis SDF.

ChrisH

[ollypenrice]

I used to get excellent planetary views with my TV Genesis, a very old scope. It would happily go to 200X so I suspect you've had bad seeing.

Olly

[Bender]

Not sure if part of the problem could be that I observe from my London suburban garden. I found 8mm a consistent limit when I was looking for a sharp image of Jupiter. I was able to use my Nagler zoom with 6 and 5mm on the moon but the image was boiling in and out of focus, but it was still ok to observe details.

Maybe I am just to fussy when it comes to a steady image

[YKSE]

Maybe this one explains something?

http://neilenglish.net/why-the-classical-achromat-produces-the-most-stable-images/

[John]

I have a Vixen ED102 which is F/6.5. It's got a nice Japanese ED doublet objective lens, not quite in the same league as the TV102 but not far off I would think.

I find 150x - 200x very regularly usable with it on the planets and have pushed to 225x on binary stars and the Moon with satisfying results.  

I observe from the edge of a town so have some light pollution to contend with though maybe not as much as you do.

Under good conditions and assuming that it's in collimation and has cooled I'd expect a scope with the optical quality of the TV102 to be able to handle up to 200x with relative ease. 

Despite Neil English's interesting piece on long, slow, achromatic refractors linked to above, he was also very impressed with the TV 102 when he reviewed it himself here:

http://www.cloudynights.com/item.php?item_id=1836

You will notice that Neil was using the Tele Vue Nagler 3-6mm zoom which you have to test the high power capabilities of the scope and did not find it wanting.

In short, if your TV 102 cannot show clear images above 110x in decent seeing conditions and assuming that it is firmly mounted, then I'd suspect that it might need an optical service.

[andrew63]

Totally agree with above.  I have a cheap Chinese 4" ed, and although not a great planetary observer these days, I get a very nice sharp view of Jupiter with a 6 BGO - around x120 which is enough for me for a look at transit red spot etc. 

 Your hand crafted TV 102 with 3-6 zoom should be enough to bring tears to the eyes !

andrew

[lensman57]

I am trolling for some inputs for a potential addition to my TV102 for planetary. I am generally quite satisfied but have sometimes a natural craving to be able to increase magnification.

I feel that i am most of the times stuck with my TV 8mm (110x, ep 0.9) plossl as the best magnification before the image starts to blur and becomes unstable on Jupiter and moon.

My theory is that a bigger apperture should give me higher mags for an ep of 1mm and hopefully enable me to push the magnification to say 150-180 before the image gest blurry.

I am a strickt visual observer with alt az mounts and dont have to much space at home, limitting the options somewhat plus with certain limits on my available time a 2h cooldown for a big Mak Cas would not be ideal either. I was thinking a 8" f6 newt on my AyoDigi mount or a C8 might be nice but i read different views on what improvements i can expect.

Hi,

I also tend to agree with others hat with an Apo particularly a fine one such as the TV provided that seeing allows a magnification of up to 60X per inch of aperture is possible without image degradation ( this is one of the main reasons for going for an APO ) , this is against 30X for the average Newt or slightly higher for Scts. Is it a possibility that you could have the scope examined by a specialist before forking out on a new scope?

A.G

[NGC 1502]

Hi Bender.  My TV Pronto is good to 120x on the planets, and it's a 70mm ED, rather than your TV 102 Apo.  As already said, I'd expect your 102 to be a great planetary scope.

I'd have a few sessions before making decisions.

If needed, TV refractors can be user collimated, lots of threads on 'Cloudy Nights' show how.  But before you even consider that, please make sure it's not viewing conditions spoiling the view.

Regards, Ed.

[Caldwell14]

I have a Vixen ED102 which is F/6.5. It's got a nice Japanese ED doublet objective lens, not quite in the same league as the TV102 but not far off I would think.

I find 150x - 200x very regularly usable with it on the planets and have pushed to 225x on binary stars and the Moon with satisfying results.  

I observe from the edge of a town so have some light pollution to contend with though maybe not as much as you do.

Under good conditions and assuming that it's in collimation and has cooled I'd expect a scope with the optical quality of the TV102 to be able to handle up to 200x with relative ease. 

Despite Neil English's interesting piece on long, slow, achromatic refractors linked to above, he was also very impressed with the TV 102 when he reviewed it himself here:

http://www.cloudynights.com/item.php?item_id=1836

You will notice that Neil was using the Tele Vue Nagler 3-6mm zoom which you have to test the high power capabilities of the scope and did not find it wanting.

In short, if your TV 102 cannot show clear images above 110x in decent seeing conditions and assuming that it is firmly mounted, then I'd suspect that it might need an optical service.

Yep, I would go along with all of that. I use a 6 mm Radian as my stanard planetary ep before going up to 224x with a 4.8mm when the seeing is uber good, and my God has it been amazing good recently, Jupiter would knock your socks off, by far the sharpest views I ever saw.

[Bender]

To be fair to the scope, it probably doesnt help that due to time constrains i would just take the scope out from the warm living room onto the partio behind the house and sit down to observe for an hour.

When i tried the Nagler zoom with 6 and 5mm on the moon i had fleething moments of sharp images when it boiled in and out of focus.

BillP on CN also replied to my question that with an exit pupil of 0.9 that the 8mm plossl creates not to far of his ideal of 0.75 and the TV102 not being a true colorfree apo it might just be my eyes not being to comfortable with exit pupils below 1mm.

Guess i ave to find an oportunity with our showery weather at the moment to leave the scope out for some time to properly cool down and test. Is there a simple way to spot faulty optics and who here in Surrey or Kent would be the best person to deal with it.

[John]

To be fair to the scope, it probably doesnt help that due to time constrains i would just take the scope out from the warm living room onto the partio behind the house and sit down to observe for an hour.

When i tried the Nagler zoom with 6 and 5mm on the moon i had fleething moments of sharp images when it boiled in and out of focus....

This might be the principle culprit. When I first got my Vixen ED102 I was surprised how the image quality improved noticeably at higher magnifications after the scope has been cooling for 40 minutes or so in the winter. In the warmer parts of the year this is reduced to 20-30 minutes.

Prior to the ED my experience had been 4" achromatic refractors which seemed to cool down really quite quickly but the little Vixen definitely needs quite a lot longer. 

I now know that the lens elements in a fast ED scope are quite a lot thicker than those in a slower achromat so there is more mass to cool and the tube wall of the Vixen (and I guess the Tele Vue) is thicker than the achromats I'd owned which I reckon slows down the temperature equalisation. Neil English has also published his view, supported by some evidence, that the glass types used in achromats retain their figure better as they cool so that could be a contributory factor as well.

Whatever the exact causes are, I have found that these ED doublets (I have an ED120 as well) need some time to cool down before they will deliver their best high power images. Not as long as a compound scope such as an SCT or maksutov-cassegrain, but some time nevertheless.

[ronin]

Any chance you could drop into The BSIA at Regents Park on night they meet?

Sure someone could help or check the Guildford Observers they have observing sessions for people to come along and get help. For the chance to look through a TV 102 I would suspect several would be more then happy to help.

[nightfisher]

Letting the scope cool for an hour will make a difference, i find my Tal100rs will give stunning planet views, but will be a little mushy till it has cooled this will do x200 on a good night