Louis D

18 hours ago, Alan White said:

Ben Nevis, when is it out of cloud?

It probably has weather very similar to our Mount Washington in New Hampshire.  Most of the times I've been to the top, it's been socked in with clouds.

27 minutes ago, markse68 said:

my understanding of optics is pretty non-existent but I’m keen to learn. How can adding another lens at the eye end of an ep increase the light throughout of that eyepiece?

By compressing the amount of existing light into a smaller image circle.  The absolute amount of light remains the same, but the amount of light per unit area increases.  Basically, it's a focal reducer that increases the focal length and exit pupil while decreasing the AFOV.  TFOV remains the same (or close to it).

1 hour ago, Realtimedoctor said:

With all due respect, but a lot of information in this is not correct. 

1. A Standard 200P will do just fine with prime focus imaging. You don't need to move the mirror up or down anywhere in the scope. (the 200P comes standard with a T2 thread for direct attachment to a T2 adaptor) 

2. You don't need to add any extensions tube for visual if switching between camera and eye pieces. 

3. I've DSLR, guidecam, auto focuser and a tec cooling device all attached to the 200P and mounted on a EQ5. Last session over 3 hours of 5 mins subs, I discarded 3 subs in total. Not sure where you are getting the 40% number from. 

4. I agree EQ5 and 200P are more suitable for visual astronomy, but payload of a mount isnt everything. You need to factor in your pixel scale of your setup, and if that is under your guided RMS there is no reason why you can't get the same image with this setup instead of a ££££ setup. 

 

After a meridian flip, how big of a deal is it to get the spider vane spikes of stars realigned with images from before the flip when imaging with a Newtonian?

Not to mention it rhymes with slough in American pronunciation meaning a swampy drainage or marsh.  We had one on our acreage that never dried out.  Anything with wheels would get stuck in it when trying to traverse it.  When I first heard about slew rate in electronics, I was mystified as to why you would use the same word for something totally unrelated.  I had no idea at the time that the swampy usage wasn't spelled slew since that's the most obvious way to spell it, just like threw, brew, or shrew.

I was going to say, can't you use multiple frames to detect stars because they move in a deterministic manner within and between images?  I'm not familiar with the 3D data set idea, but if all the comet data does end up in a single plane, it should be fairly simple to remove everything not in that plane (the stars).  That, or squash them all into a single point each within the comet image plane so the stars are pinpoints instead of trails.

1 hour ago, merlin100 said:

Yes. Do you have a nickname for the mailman? 

Mailman is probably it since postman is the formal as in the movie title The Postman Always Rings Twice.  In your original sentence, we would have probably just said "Look what showed up in the mail today!" or "Look what showed up on my doorstep today" since we rarely see our postmen because our mailboxes are all centralized at the back of the subdivision, and because many packages arrive via UPS, FedEx, or Amazon delivery directly at our doors nowadays bypassing USPS.

51 minutes ago, michael.h.f.wilkinson said:

Some stellar residues can be seen

Just looks like imager noise, so not a big deal for most viewers.

I kind of like the effect of not having star streaks in the image distracting from the comet.

On 28/06/2020 at 07:28, merlin100 said:

This arrived care of the postie around 8.45am, this morning!

Off topic, but is postie a common nickname for a postman in the UK?  I've never heard the term used anywhere in the US.

19 hours ago, Ken82 said:

Should I get some risers for my telrad ? It’s quite close to the finder scope. 
 

also could do with a coma corrector, which one ??

If you get a Telrad riser, how are you going to use the RACI without going around to the other side of the scope?  It seems like it would be a wall between the focuser and the RACI.

I use a GSO/Revelation coma corrector to good effect in my Dob.  I had to add a 25mm spacer ring between the eyepiece holder and the optics section for best correction.  It requires about 11mm of in-focus and adds 10% magnification.  Your eyepieces also need to focus within about 5mm of the eyepiece shoulder for best correction.  Only my 12mm NT4 required parfocalization since it focuses 19mm below the shoulder.  It also made it so much easier to swap it in and out by minimizing refocusing.

I've got two Synta 127 Maks, one Orion branded, one Celestron branded, and neither has any focus backlash and both were well used when I bought them.  I would return that scope straight away as that is not right to have focus backlash like you describe.

4 hours ago, PEMS said:

The standard 200P will not immediatly allow images, the mirror will have to be moved up the main OTA tube so that the prime image from the mirror can reach the camera sensor. So that would then mean a complete recolloimation of the scope.

I'm able to reach focus with my Dob (low profile focuser) using the GSO/Revelation coma corrector.  It's how I was able to take this photo of a Mercury transit at prime focus with a DSLR:

54 minutes ago, John said:

There's our problem in the UK then - our highest point is just 1345m and that is Ben Nevis in the Scottish Highlands !

From what I know of Ben Nevis, you probably wouldn't want to be observing from its summit, either.  You were higher than that when you were visiting the plains of northern Arizona!

The 25mm BST is not very good at f/6 from 50% out.  It does have plenty of eye relief for eyeglass wearers.  The 24mm APM UFF is much more consistent across the field and is quite usable with eyeglasses.  If you expand the FOV image, you'll see that the BST tends to blur out sooner than the HD-60 and much sooner than the UFF.

31 minutes ago, barkis said:

Just hope any slew speed glitches don't qualify your
mount for Centrifuge duty at Nasa. 😬
Ron.

Like this?

In this case, it might be the expense of making a specialized triplet that limits the design from being mass produced.

Indeed, my 2011 vintage Delos 10mm arrived with the traditional dual sided cap.

I always go by lowest power (25x to 40x), mid power (65x to 90x), and highest power (150x to 220x) and then do the math for the particular telescope to figure out what eyepieces make sense.  Certainly, there is plenty of room to fill in the blanks at the higher end of the power range when poking at the limits of seeing.

3 hours ago, paul mc c said:

Its actually visible just after sunset right through to sunrise at the minute.

I suppose if you're far enough north it is, but not from here.  It is technically visible all day from here, but good luck seeing it through a blue sky.

18 hours ago, Don Pensack said:

DEW.  It will form on a mirror pointed at the sky, but not on a mirror pointed at trees or buildings.

It will affect the secondary first, but also the primary.

Now, if you have fans, the scope can be horizontal and still cool just as well without risk of dew.

Never had that issue in Texas, not even on my 127 Mak.  Perhaps because I don't observe in the mornings when the air temperature is closer to the dewpoint.  I've never felt the slightest need for dew strips or shields.

17 hours ago, Stardaze said:

So who’s measured theirs?

Did you mean entrance pupil of the eye?

In digital design, slew rate is the speed at which a device transitions from 0 to 1 or 1 to 0.  There's no pivoting involved at all, so explain that one. 

1 hour ago, gary756 said:

Anyway the zoom ep was good eye relief I found to be comfortable even on max zoom.

With or without eyeglasses?  I've had trouble using them with eyeglasses at star parties, so I haven't bought one myself.

2 hours ago, bomberbaz said:

Helps keep your mrrors cleaner longer louis

I just avoid going out on nights with significant particulate matter in the air, like on night of the 4th of July (fireworks residue), when my neighbors are burning logs in their fireplaces, backyard grilling, or are running their smokers overnight.  The rest of the time, the level of airborne particulates hasn't been much of an issue for me.

2 hours ago, Barry-W-Fenner said:

Out of interest, Do you all cool your dobs with the covers obviously off and at a horizontal position, Or say 45 degrees.

I cool mine straight up and down like a chimney.  I don't know what advantage tilting it would provide.

I've used a cheap M&SG filter to cut sunset haze a little bit to detect other horizon hugging comets in the past.