Image of the day

From the
ATWB Customer Gallery

Gray Jay

My Account

New to Astromart?

Register an account...

Need Help?

Posts Made By: Dmitri Kulginov

November 20, 2004 01:01 PM Forum: Equipment Talk

12.5 mm Ultima or UO Ortho?

Posted By Dmitri Kulginov

Thanks for the replies!

Perhaps I should elaborate on orthos. I have a 4mm UO ortho that I love dearly, and don't find the tight eye relief to be a problem - as long as the exit lens is small and fits between the eyelashes. I guess the lens is small enough all the way to 9mm. At longer FL the lens becomes larger, but so does the eye relief. I'm pretty sure that at 18mm the eye is farther away from the lens than the eyelash length, but at 12.5mm I'm not so sure. I've got a Surplus Shed 12mm eyepiece that is pretty good, but has this problem - I have to clean it rather often.

Anyone with long and greasy eyelashes?

Dmitri

November 24, 2004 07:12 AM Forum: Solar System Observing

Craterlets in Plato

Posted By Dmitri Kulginov

Do they ever look lighter than the floor? If yes, at what Moon phase?

Do they ever look darker?

Dmitri

November 27, 2004 09:41 AM Forum: Equipment Talk

UO 2x 1.25" Barlow

Posted By Dmitri Kulginov

Please, someone who has used or seen this Barlow (not Klee!), share your impression!

Hopefully,
Dmitri

December 6, 2004 01:22 AM Forum: Deep Sky Observing

NGC7331

Posted By Dmitri Kulginov

Yesterday I finally got a chance to try out my new Ultima 18mm eyepiece after ten cloudy nights. When I got out, Pegasus was well placed in the sky and I decided to take a prolonged look at 7331. I could detect it already at 11x; at 22x (with 18mm) it was quite obvious, position angle and all. Since comparing different eyepieces was my business, I spent at least 40 minutes just looking at the galaxy at different powers. Gradually an overall impression had begun to cristallize, but then came the clouds.

When I came home I checked the entry about this galaxy in the O'Meara book about Caldwell objects (an excellent book in every respect!). My impression was rather close to the photo, a bright core surrounded by extended elongated haze. There was way to go to O'Meara's sketch showing the spiral arms, but he had spent several hours with this galaxy! (Having a bigger scope and darker skies as well.)

Dmitri

December 8, 2004 06:00 AM Forum: Deep Sky Observing

Open clusters and nebulae

Posted By Dmitri Kulginov

Yesterday we were blessed by the first clear night in almost two weeks. 80mm of aperture is unimpared when it comes to open clusters, and I spent a couple of hours looking at OC and DN. The find of the day was NGC7209, a very delicate open cluster in Lacerta. It looks very small at low power, but resolves into a lot of "small" (in Herschel sense of the word) beautiful stars that fill my field of view at 100x (27 arc min). I failed to find much beauty in M39 again, but was fascinated by M34 with its pagoda shape. Nebulosity in NGC281 looked exactly as in the book at 22x. Merope nebula was kind of easy with UHC (I guess the filter kills most of the light pollution even this is a reflection nebula - as Inge has noted here).

In the end Orion had risen high enough and I looked at M42/M43. The night was dark, and the nebula was so large and bright that I almost fell over! The best view was at 22x (my new 18mm Ultima), it was great both with UHC and unfiltered, with Trapezium well resolved. I still strongly suspect that we cannot see all its splendour at this latitude (57N)... After that I checked Rosette nebula - and saw it for the first time. I couldn't make out the shape, but when I moved the scope away from the central cluster, the sky suddenly would become jet-black. Finally I tried to see it with naked eye through the UHC filter - and saw it as an "out-of-focus star". It disappeared without the filter.

Dmitri

December 10, 2004 05:42 AM Forum: CCD Imaging and Processing/Solar System

WYSInotWYG

Posted By Dmitri Kulginov

I am yet to see an astrophoto that can be favourably compared to what can actually be seen at the eyepiece. The most striking are pictures of Milky Way that look more like those of a firework. It is obvious that the faintest parts of, say, faint nebula stand out much more in a photo, but the brightest parts are [ almost ] always overexposed and void of detail. The human eye has much wider dynamic range than film or CCD. My challenge is: why don't you, sophisticated astro-imagers, try to mimic the visual perception?

The most obvious way would be to make a composite image where the brightest parts are taken from a shorter exposure, and the faintest parts from long exposure are played down to some reasonable level so that they don't jump on you. Also colours should be corrected - no red!

Modestly,
Dmitri

December 13, 2004 06:33 AM Forum: Deep Sky Observing

NGC6939/6946 in small aperture

Posted By Dmitri Kulginov

Yesterday I looked at this open cluster and its ghost, a face-on galaxy in the same low power FOV, on the border between Cepheus and Cygnus. I started to see traces of faint stars in the cluster at 22x, and could resolve about ten stars in the cluster at 127x. I didn't see the galaxy as such, but I could tell that the sky colour was not as black between the two mag 10 stars where the galaxy is supposed to be, as it was black elsewhere. With this approach, it was hard to estimate the size.

A few days earlier I went outside with a 10x50 binocular for a quick look, and I think I saw them both. The binocluar was hand-held and shaking, and this, together with the low power, made it a little easier.

Anyone looked at this pair with small aperture lately?

Dmitri

December 15, 2004 05:32 AM Forum: Telescope Making

To make a good mirror

Posted By Dmitri Kulginov

Perhaps a silly question...

What does it take for a newbie to make a 8" mirror no worse than 1/8 wave? Special abilities, price of materials, amount of spoiled blanks, any measuring equipment, how many hours?

Is it possible at all?

Dmitri

December 19, 2004 02:54 AM Forum: Equipment Talk

New GSO dobs

Posted By Dmitri Kulginov

They use roller bearing for azimutal motion and cost 100 Euro more. How are they? Has anyone compared them with the old ones?

Dmitri

December 22, 2004 07:32 AM Forum: Equipment Talk

Binoviewers and limiting magnitude

Posted By Dmitri Kulginov

This is not really the most appropriate forum for my question, but that's where the most binoviewer owners are smile

When discussing limiting magnitude, practically everybody says that looking by both eyes through a binocular (not binoviewer) provides twice as much light and hence a binocular corresponds in light gathering capability to a telescope of an aperture sqrt(2) times larger. This should supposedly increase limiting magnitude by 2.5*log(2) = 0.75 for the same aperture.

These statements have always striken me as careless. Brain doesn't just add up the light that comes from two eyes, it makes something very complicated that makes people love binoviewers, even though a binoviewer does not provide any additional light but shares the same amount of light between two eyes.

So my question to all owners of binoviewers who have a computer star atlas that shows accurate magnitudes of faint stars: does use of a binoviewer change telescopic limiting magnitude? Can you see deeper when you use a binoviewer as compared viewing without binoviewer and with the same eyepiece? If yes, how much deeper? If we follow the logic that I mentioned above, limiting magnitude through a binoviewer should decrease because the total amount of light is the same minus additional loss in prisms.

Another question: if you look in the binoviewer and then with one eye in one half of the binoviewer, do the faintest stars disappear? If yes, how much you do loose in limiting magnitude?

Dmitri