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Posts Made By: Jarad Schiffer

April 14, 2004 08:21 PM Forum: Equipment Talk

Add a Refractor?

Posted By Jarad Schiffer
For a relatively cheap refractor that is good on planets, I wold suggest the Orion ED80. But, it is still an 80mm refractor, so your 8" reflector should beat it quite handily. The real reason for going to a small refractor isn't that it will give better views than your 8", but that it will be a lot quicker and easier to set up. You would have to get a 5-6" APO or long fl achro to match a decent 8" reflector, neither of which meet your twin requirements of relatively cheap and mountable on the SVP.

So if you want better views, stick with the 8" you have. If you want a quick-look set up, get the ED-80 or something similar (maybe a 5-6" mak, since you are only using it for planets). Although if you get the ED-80, it also makes a nice widefield companion to your 8" under dark skies....

Jarad

April 26, 2004 05:04 PM Forum: Telescope Making

Heater question

Posted By Jarad Schiffer
Astrosystems sells a heater that has 2 temperature sensors - 1 in the air, and 1 on the mirror. You set it to keep the mirror ~1 degree above ambient (adjustable to even less if you want). That way it turns itself on and off as needed to keep the mirror just warm enough not to dew. I have used this system on 2 scopes now - it works very well.

Jarad

May 5, 2004 02:50 PM Forum: Eyepieces

low power 1.25'' wide field

Posted By Jarad Schiffer
Rod is right. I have looked through an SWA and a Widescan III - they suffer from off-axis astigmatism in fast scopes (stars appear as "seagull" towards the edge of the field). The Panoptic does not have this problem. I haven't used the Axiom or Antares, but have read reports that they also suffer in fast scopes. I have heard that the Speers-Waler actually does pretty well (but not seen one myself). The other ones you haven't listed would be a Pentax XL 21 or XW 20, both of which will be able to handle the fast optics, but are quite pricey.

Hope this helps,

Jarad

May 14, 2004 08:08 PM Forum: Telescope Making

Off Axis fantasy

Posted By Jarad Schiffer
The light loss you thinking of in this case is due to magnification - 2x the focal length means 2x the mag, 4x the area, so 1/4 as bright (for extended objects). For an 8" f25.5, you won't be able to get much more than a 1/2 degree field with a 2" eyepiece, and not much below 100x (or higher, depending on whether you do it with a 55mm plossl or a 41 pan or a 31 nagler....). This won't be a wide field instrument.....

Jarad

May 26, 2004 03:06 PM Forum: Equipment Talk

Televue 3-6mm Zoom or 3.5 Nag ?

Posted By Jarad Schiffer
Do you wear glasses? The eye reief on the 3-6 zoom is significantly tighter than on the nagler T6's. If yuo don't wear glasses you could try the zoom, but if you do that will make the useable field even narrower, and I would definitely go for the 3.5 T6.

Jarad

June 1, 2004 02:09 AM Forum: Equipment Talk

Who makes high quality newtonians?

Posted By Jarad Schiffer
Starmaster is about to offer an 8" newtonian solid OTA (no mount). Hard to beat a Zambuto mirror. Otherwise I would say build your own with a Royce mirror (or one of the other preimum mirror makers - Swayze, Mark Harry, etc.).

Jarad

June 2, 2004 01:47 PM Forum: Equipment Talk

focuser travel problem with Paracorr

Posted By Jarad Schiffer
The paracorr does require an extra 1/2" of in-travel compared to without the paracorr. If you are using 1.25" EP's, you can get a low profile 2"/1.25" adapter that will give you most of it. For 2" EP's, try raising the primary on it's collimation screws like Floyd suggested.

Jarad

June 7, 2004 01:42 PM Forum: Equipment Talk

Planetary images using a Swayze mirror ?

Posted By Jarad Schiffer
There are growing number of mirror makers who you pretty much can't go wrong with. Swayze is one of them. Some of the others include Zambuto (only available in Starmaster, Portaball, or Teleport scopes), Pegasus, Royce, and Mark Harry.

If you are making your own scope, Steve is also a great scope maker, and a nice guy. He will probably give you lots of advice on how to build the rest of your scope too, if you want it.

Jarad

June 8, 2004 05:24 PM Forum: Telescope Making

Secondary size

Posted By Jarad Schiffer
For a 16" f4.7, assuming visual use only, an 18" tube ID and a 1.6" focuser, I would use a 2.6" secondary. If your tube is wider or focuser taller, you may need to go up to a 3.1". For planetary only use, you could go down to 2.14"

For a 12" f5.8, visual only, 14" ID, 1.6" focuser, I'd use a 2.14" secondary, although you could get away with a 1.83" if you want primarily planetary use. Again, a wider tube or taller focuser may make you bump it up to 2.6".

For photography, you would need to go up a few sizes for both, depending on how wide you want your non-vignetted field to be.

To play with the numbers yourself, download Newt 2.0 from:
http://home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm

Hope this helps,

Jarad

June 9, 2004 05:08 PM Forum: Telescope Making

Secondary size for 12.5 f/6.4

Posted By Jarad Schiffer
You have set it for a 1.25" focuser. Is that what you are going to use? If so, then you can get away with the 1.52", but this is going to be a narrow-field instrument... It is also going to be tall, so you will be using a ladder. Is this a dedicated planetary scope? If so, that should work.

For a general use scope, I would make it a bit faster (pick an f-ratio that will allow you to observe without a ladder - probably f5.x, depending on your height). I like wide fields, so I would go with the 2.14" secondary for a decent illuminated field (that's still just 17% CO, not bad at all, and you won't see a huge improvement below that). But that's me, not you. The 1.83" secondary would still do okay in a 2" focuser, just a bit of vignetting in the lowest power eyepieces (like the 35 Pan, etc.).

Jarad


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