Need to know what certain parts are on a telescope are

On Aug 25, 10:54*am, Martin Brown
wrote:
On 25/08/2012 12:59, wrote:









On Aug 25, 4:12 am, Martin Brown
wrote:
On 24/08/2012 23:01, Yousuf Khan wrote:

It came with 3 eyepieces: an SR4mm, an H12.5mm, and an H20mm. What
situations are these used for?

Almost never, higher magnification, medium magnification.

And with the 3x Barlow lens: Never, Never and highest magnification.

The 3x Barlow and 4mm eyepiece are intendeed to allow manufacturers to
claim up to 500x magnification or some such absurdity. It is rare to use
much over 20x per inch of aperture (maybe twice that on double stars).
try them out and see for yourself.

The more reputable vendors generally do not even include a Barlow,
supplying instead a reasonable quality eyepiece or two. However, the
OP's telescope might perform quite well with a high-quality Barlow
purchased later, assuming that iit is not used to obtain mags over 50x

Not with those eyepieces.

A 2x Barlow would turn the 20mm into a 10mm, probably pushing 75x
-100x depending on the primary FL.

I don't understand why makers don't provide
beginner sets in the golden ratio and with a 2x Barlow - it makes so
much more sense and gives a wide range of useful magnifications.

The low-end vendors seem to buy the eyepieces, or at least the lenses
that go into them, from just a few suppliers, who all seem to make 25,
20, 12.5, 6, 5 and 4mm FLs.

eg 26, 16, 10 and with Barlow 13, 8, 5 all of which are useful.

His best buy before anything else would be a 32mm plossl without a
doubt.

Possibly, however we do not know enough about his scope in order to be
sure. If his focuser is a 0.965, his eyepiece selection will be
severely limited. However, even a 25 mm Plossl would give fine low
power views. I have an old 30mm Plossl which works well, but I use
shorter EPs much more often.

Or an A4 sheet of Baader visual solar screen.

That would be useful.

per inch. *BTW, most scopes can handle much more than 20x per inch.
(Your scope might be different.)

Smaller scopes can be if you don't mind empty magnification but larger
ones tend to be seeing limited to about 1" arc fwhm most of the time at
least in the UK under the jetstream. Unless the seeing is exceptionally
good I don't have much use for anything above 25x per inch.

Seeing varies from moment to moment, I find that 35x per inch is good
for planets most of the time.

I routinely used 140x on a 3-inch, no problems except the FOV seemed
rather small.

I also suspect that the sort of scope that comes with 3x Barlow, Huygens
and 4mm Ramsden eyepieces is not going to be truly diffraction limited
or particularly free from false colour.

The real problem could turn out to be the mount, which might not be
suitable for higher mags regardless of other considerations.

In article ,
Yousuf Khan wrote:

On 23/08/2012 12:38 PM, Chris.B wrote:

snip

2) A Barlow lens is an image magnifier.

3x larger may be too much for most telescopes.

Since it magnifies errors of alignment, mounting vibration,
atmospheric problems, optical inaccuracy, reduces field of view,
increases difficulty of pointing and greatly reduces the brightness of
the final image. The "fuzzy blob syndrome" is typical of inexpensive
telescopes and over-ambitious beginners.

So the Barlow lens would be overkill?

You haven't mentioned the aperture and focal length of the 'scope, both
of which are important to the choice of eyepiece. Magnification (without
the Barlow) is the focal length of the objective (primary mirror)
divided by the focal length of the eyepiece. The common rule of thumb is
that, under ideal conditions, the maximum useful magnification is 2X per
millimetre of objective, or 50X per inch.

For example, a 4.5" (114 mm) f/8 mirror, typical for a small Newt, has a
focal length of about 900 mm. It will allow a maximum magnification of
about 225X, which is what a 4-mm eyepiece will give, or a 12-mm when
coupled with a 3X Barlow.

If your primary is similar, your selection of eyepieces will give you
about 45X, 72X, & 225X, or with the Barlow 135X & 216X -- but forget
about the notional 675X from the highest-power eyepiece coupled with the
Barlow.

--
Odysseus

On 24/08/2012 9:44 PM, Chris L Peterson wrote:
On Fri, 24 Aug 2012 17:56:21 -0400, Yousuf Khan
Second, what's a good eyepiece for taking pictures with a digital camera?

If you have a DLSR, no eyepiece at all is best, you just do prime
focus imaging. If your camera doesn't have a removable lens, you can
do afocal imaging through almost any eyepiece, you just need some sort
of adapter to mount your camera to the telescope body or eyepiece
holder.

Well, I am talking about a non-DSLR, so what sort of adapters are
available for mounting a non-pro digital camera to an eyepiece?

Yousuf Khan

On Saturday, August 25, 2012 8:55:49 PM UTC-7, Yousuf Khan wrote:
On 24/08/2012 9:44 PM, Chris L Peterson wrote:

On Fri, 24 Aug 2012 17:56:21 -0400, Yousuf Khan

Second, what's a good eyepiece for taking pictures with a digital camera?



If you have a DLSR, no eyepiece at all is best, you just do prime

focus imaging. If your camera doesn't have a removable lens, you can

do afocal imaging through almost any eyepiece, you just need some sort

of adapter to mount your camera to the telescope body or eyepiece

holder.



Well, I am talking about a non-DSLR, so what sort of adapters are

available for mounting a non-pro digital camera to an eyepiece?



Yousuf Khan

Well, it is really hard to pry necessary info from you. We really need to know what size those eyepieces are; 0.965, 1.25 or 2.00 (all in inches)? Without this knowledge, it will simply take longer to answer your questions. Also, the aperture and focal length both figure into magnification calculations...

For example, this would work...

http://www.skiesunlimited.net/celest...-universal.htm

... but NOT for 0.965 eyepieces, without an adapter, if such a thing is even made.

\Paul A

On Sat, 25 Aug 2012 23:55:49 -0400, Yousuf Khan
wrote:
Well, I am talking about a non-DSLR, so what sort of adapters are
available for mounting a non-pro digital camera to an eyepiece?

Probably none which is suitable to your particular camera and your
particular eyepiece. There are just too many different such cameras
out there. Your best bet is probably to try to construct such an
adapter yourself. It's probably easier to buy a new camera to which
there is an adapter.

Is it possible to attach filters to your amateur (non-pro) non-DSLR
digital camera? If so, that might be a way to find an adapter to your
camera. If not, all bets are off.

On 26/08/2012 07:17, Paul Schlyter wrote:
On Sat, 25 Aug 2012 23:55:49 -0400, Yousuf Khan
wrote:
Well, I am talking about a non-DSLR, so what sort of adapters are
available for mounting a non-pro digital camera to an eyepiece?

Probably none which is suitable to your particular camera and your
particular eyepiece. There are just too many different such cameras out
there. Your best bet is probably to try to construct such an adapter
yourself. It's probably easier to buy a new camera to which there is an
adapter.

Is it possible to attach filters to your amateur (non-pro) non-DSLR
digital camera? If so, that might be a way to find an adapter to your
camera. If not, all bets are off.

There are plenty of adapter out there for the birder market - the
keyword is digiscoping (horrid I know) eg

http://www.actionoptics.co.uk/Telescopes.htm

But without an equatorially driven scope I wouldn't bother. You can
probably get better results with a suitable cheap webcam and registax or
carefully holding the camera up to the eyepiece with live view enabled.

--
Regards,
Martin Brown

In article
,
Odysseus wrote:

snip

[...] The common rule of thumb is that, under ideal conditions, the
maximum useful magnification is 2X per millimetre of objective, or
50X per inch.

P.S. Another way of stating this rule is that the shortest focal length
of a useful ocular, in millimetres, is half the objective's focal ratio.

--
Odysseus

On 26/08/2012 1:04 AM, palsing wrote:
Well, it is really hard to pry necessary info from you. We really
need to know what size those eyepieces are; 0.965, 1.25 or 2.00 (all
in inches)? Without this knowledge, it will simply take longer to
answer your questions. Also, the aperture and focal length both
figure into magnification calculations...

That's because it's hard to find the information. Looking through the
manual (really just a pamphlet):

focal length: 700mm f/9
eye-pieces: SR4mm, H12.5mm, H20mm
Apertu 76mm (3")
3X Barlow lens, 1.5X Erecting lens.

Yousuf Khan

On Wednesday, August 29, 2012 10:38:06 AM UTC-7, Yousuf Khan wrote:
On 26/08/2012 1:04 AM, palsing wrote:

Well, it is really hard to pry necessary info from you. We really

need to know what size those eyepieces are; 0.965, 1.25 or 2.00 (all

in inches)? Without this knowledge, it will simply take longer to

answer your questions. Also, the aperture and focal length both

figure into magnification calculations...



That's because it's hard to find the information. Looking through the

manual (really just a pamphlet):



focal length: 700mm f/9

eye-pieces: SR4mm, H12.5mm, H20mm

Apertu 76mm (3")

3X Barlow lens, 1.5X Erecting lens.



Yousuf Khan

Well, OK.

Measure the eyepiece barrel diameter, it will be either just under one inch, 1-1/4 inch or (very unlikely) 2 inches. Only then can any suggestions be made regarding mounting a camera in front of the eyepiece.

\Paul A

On Wednesday, August 29, 2012 10:38:06 AM UTC-7, Yousuf Khan wrote:

That's because it's hard to find the information. Looking through the

manual (really just a pamphlet):



focal length: 700mm f/9

eye-pieces: SR4mm, H12.5mm, H20mm

Apertu 76mm (3")

3X Barlow lens, 1.5X Erecting lens.

Considering the above descriptions, I can almost guarantee they're 0.965"
eyepieces, which is (or at least was 50 years ago) the standard size for
microscope eyepieces. No one I know of anymore makes Huygens or Symmetrical
eyepieces in 1-1/4". By the way, you can put the Barlow away... The
magnification it can provide with your setup is way too high for what it can
possibly use.