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which apo?

skye at night

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skye at night

skye at night

Posted
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hello,

having been refractorless for a couple of years , i feel it is time to get 'back in' and get a decent fast apo...

there are 2 candidates...

i have option on 2 second hand scopes..

1- a TMB 92ss f5.5

and/or

2 - a Pentax 100 sduf II f4

same price.... both quality.

Mainly for AP.

But just can't decide which..

any advocates/owners of/for either?

Thanks

Steve

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skye at night

skye at night

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Nobody with experience of either???

Erring towards the Pentax at present as i can't resist that extra fast glass..

Plus.. there seems to be some QC issues with the TMB's that are now made.. ie post Tom Back era...

Shame.. as on paper they are the dogs'..

Steve

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AndyH

AndyH

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Note to self: fully read post before replying ;)

I'm not an imager. Purely for the rarety factor, I'd plump for the Pentax.

Cloudy Nights would be the place to ask, if you haven't already. But be wary. As I'm sure you know there are terrible refractor snobs/bullies on there.

F4 is REALLY fast ;)

Cheers,

Andy.

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skye at night

skye at night

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Yes Andy..

i only ever 'lurk' on CN.....

Having seen a few 'deep' arguments on there.. I dont really want to get involved..

Noticed you are in paisley...

going back soon to visit the family, most of whom live there.....

Do you 'frequent' the Coates Observatory much?

Not been for years, My first 'real' view of Saturn was through the main scope there...

Steve

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David Pavlich

David Pavlich

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As someone who has over 9000 posts on CN, you can bet that the most defensive group is the diehard refractor guys. They can't get past the laws of physics. ;) However, there are some VERY well versed refractor owners there. I have 2, but I still believe that a 6" apochromatic refractor can't outdo a 14" SC. But you sure will get arguments to the contrary there. ;)

Anyway, for imaging, the Pentax is the winner here. At f4, you'll be pulling in photons quickly and the glass is top shelf. You won't be disappointed.

David

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dweller25

dweller25

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As someone who has over 9000 posts on CN, you can bet that the most defensive group is the diehard refractor guys. They can't get past the laws of physics. :p However, there are some VERY well versed refractor owners there. I have 2, but I still believe that a 6" apochromatic refractor can't outdo a 14" SC. But you sure will get arguments to the contrary there. ;)

Anyway, for imaging, the Pentax is the winner here. At f4, you'll be pulling in photons quickly and the glass is top shelf. You won't be disappointed.

David

David,

The laws of physics are simple. No 6" scope will beat a 14" scope, aperture rules man ;)

Unless it's a Takahashi in which case my 5" scope will wipe the floor with any mass produced 11" SCT on the planet.

Oops sorry wrong forum - thought I was on CN :)

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David Pavlich

David Pavlich

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David,

The laws of physics are simple. No 6" scope will beat a 14" scope, aperture rules man ;)

Unless it's a Takahashi in which case my 5" scope will wipe the floor with any mass produced 11" SCT on the planet.

Oops sorry wrong forum - thought I was on CN ;)

Very good! I'm a fan of the Tak refractor, so much so that I consider Tak the best refractor in the business. I get a lot of funny looks from some refractor owners, but it's hard to argue the point. Simply terrific pieces of hardware!

David

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Darth Takahashi

Darth Takahashi

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David,

The laws of physics are simple. No 6" scope will beat a 14" scope, aperture rules man ;)

Unless it's a Takahashi in which case my 5" scope will wipe the floor with any mass produced 11" SCT on the planet.

Oops sorry wrong forum - thought I was on CN :)

The problem with all these discussions is no one mentions what the criteria is that's being evaluated? ;) Then they spin out off control and eventually drop to the lowest level, flame wars!

I love my TOA130F and its a keeper, for life! no matter what anyone else thinks or says.:D

My vote goes for the Pentax as they are renowned performers.:p

Neil.

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ollypenrice

ollypenrice

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I have a guest who comes with a Pentax. It is an imaging scope, originally conceived for film, I believe. It would strike me as an odd choice for visual use since you can get a wide visual field using a wide EP and you would not have to spend a fortune on getting the f ratio down to 4. What purpose would f4 serve in visual use?

For imaging it has been surpassed by the Tak FSQs which have flatter fields and better colour correction. The Pentax is outdated and would be a good choice if this were reflected in the price. It would have to be a lot chepaer than a used FSQ1106 or Baby Q to tempt me, personally.

As for this refractor/SCT ballyhoo, it depends what you mean by 'beats.' Obviously aperture rules when it comes to collecting light. When it comes to pointing that light in the right direction it is optical quality that rules. Meade and Celestron optics versus Takahashi, AP, TeleVue, Tec... enough said. As I have said before on refractors, It ain't what you see, it's the way that you see it. The view is different and you like what you like. I like the view in an SCT and love the view in a refractor.

Olly

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Darth Takahashi

Darth Takahashi

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As for this refractor/SCT ballyhoo, it depends what you mean by 'beats.' Obviously aperture rules when it comes to collecting light. When it comes to pointing that light in the right direction it is optical quality that rules. Meade and Celestron optics versus Takahashi, AP, TeleVue, Tec... enough said. As I have said before on refractors, It ain't what you see, it's the way that you see it. The view is different and you like what you like. I like the view in an SCT and love the view in a refractor.

Olly

I think we can make it simple, I hope? Refractors win when it come down to pure image quality (Sharpness & Contrast). The large central obstruction in most reflectors reduces image contrast. In fact, RC systems shouldn't be used visually for this very reason, 35-40% central obstruction.

I hope nothing I said above is too contentious to anyone.;)

Neil.

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skye at night

skye at night

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Save yourself a packet and get a Skywatcher ED 100 or some such. If you decide to venture into astrophotography then you can contemplate getting something faster

Neil.

Been 'doing' AP for 5 years or so in some form or another....

i wouldn't be looking at the 2 scopes mentioned if that was not my primary aim...

Thanks to all who contributed...

Pentax will probably win out as i am aware also of QC issues with the Post TMB TMB's if you know what I mean...

Moocher. I will check out the Borg...

Thanks

Steve

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  • 2 weeks later...
KaStern_Former_Member

KaStern_Former_Member

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Hello Steve,

no experience with both, no astzrophotographer, just theory:

For AP go for the Pentax. It has a flat field. It is faster. The taiwanese made TMB SS

needs an additionla field flattener, the basic scope has a strogly curved field.

Will the SDUF II (much better than the SDUF!) will be good enough for your needs?

Depends on your camera (pixel size) and type of photography.

Try to find the spot diagrams for the SDUF and spherochromatism curves.

With these you can clearly decide if the SDUF is what you need.

Tele-Optic - Ihr Astronomie-Zentrum in Rhein-Main - Pentax 100 SDUF II

This page tells:

20 mycron spot size over 88mm Field size. Is that sufficient?

From that page:

https://www.optcorp.com/product.aspx?pid=8731

you can see that it is a 4 lens modified (4 lens in 4 groups) Petzval design.

Regards, Karsten

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Marmite

Marmite

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David,

The laws of physics are simple. No 6" scope will beat a 14" scope, aperture rules man :)

Unless it's a Takahashi in which case my 5" scope will wipe the floor with any mass produced 11" SCT on the planet.

Oops sorry wrong forum - thought I was on CN :(

But...don't you realise that any telescope which hasn't been blessed by the hand of Holy Saint Roland himself is nothing but junk? Especially if it's foreign. And doubly so if it's Asian!

"Ohhhhh say can you see..."

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