Second Time Around

Louis, can you measure the thread under the 30mm APM?  I'd read that it was a little larger than 43mm, and that a Dioptrx wouldn't fit.

Thanks.

Thanks, Gavin.

Thanks, Gavin, I'll have a proper look shortly.  Are these better than the cheaper models that Joko and others sell?

Any other suggestions? I'd need one that will take the Televue 55/67mm Plossl as well as narrower eyepieces.

IIRC, there was a (Japanese?) zoom available late 60s with a focal length of 8.4-21mm. I almost bought one around that time.

What smartphone adapter would you recommended and why?  If it makes any difference it's for an OVNI-M.

Cheers.

It may be worth looking at the tiny US made Photon Freedom Micro lights that  are available in different colours, including red.  Go to  http://www.photonlight.com

The Micro model can be dimmed down really low.  It can be put flat on a table, worn round the neck or clipped onto a variety of objects.  There's also an optional fingertip attachment  available.

I bought the covert model to get  the narrowest beam, but found it has uneven illumination. I don't know whether the standard version is the same. 

Can anyone help?

For those who haven't seen it, the link below will take you to a topic where I post the results comparing the accuracy of 6 (now 7)cloud forecasts, including Clear Outside.

https://stargazerslounge.com/topic/376745-a-record-of-the-accuracy-of-my-local-cloud-forecasts/#comment-4189743

I'm always worried that any cloth could have a small piece of dirt or grit on it that could damage an optical surface.

I therefore prefer Zeiss single use lens wipes. These come in a sealed packet so you can always be confident that they're uncontaminated.

I'd particularly be worried about an expensive main mirror.

My own second-hand 10 inch OOUK mirror looked so dirty I opted for the safe option and sent it to them for cleaning.  It turned out it was so bad it needed recoating.

Dark-adapted pupil size can vary hugely from person to person to say the least.   I'd therefore suggest you measure your own at your observing site.  It isn't difficult and there are several methods that a search will show you.  This is what I did.

I got dark-adapted for a few minutes to allow my pupils to dilate (there's no need for longer as full dark adaption is a chemical process).  I then got my wife to take a flash picture whilst I held a ruler just above my eye.  The flash is so fast that your pupil won't react.   Make sure though you haven't got red eye reduction or pre-flash on.

As Stu said, your pupil size will allow you to work out the maximum focal length eyepiece you can use without  effectively using a smaller aperture scope.

Unfortunately my maximum pupil size is only 4.5mm at my Bortle 4/mag 20.87 site.

I too have a 10 inch f/4.8 Dob.  I use an Explore Scientific coma corrector with mine that increases the focal length by a factor of 1.06.

So the maximum focal length eyepiece I can use without effectively using a smaller aperture scope is 4.5 x 4.8 x 1.06 = 22.9mm.  As there are few if any 23mm eyepieces, plus my pupil size is likely to get even smaller with age, I use a 22mm.

I'm further constrained as I have astigmatism and much prefer to use a Dioptrx to correct this rather than wear glasses to observe.  This does restrict the eyepieces that I can use though. 

However,  a longer focal length eyepiece is also useful for a wider field of view despite the loss of aperture - I use a 28mm/68 degree Explore Scientific, that also accepts a Dioptrx.

I'm not qualified to write reviews on astro gear, but I have had a large number of reviews published in UK fishing magazines.

I can say categorically that many of the UK fishing magazines were and probably still are influenced by their advertisers.

For instance, I once wrote a very unfavourable review of a reel from a well-known brand.  The reel wasn't very free-running, and in cold weather it almost froze up completely.  I submitted the review to several of the magazines I wrote for regularly.  Not one published it, although they published all the other reviews and articles I sent them!  

That reel was quietly withdrawn from the market.  However, that was after a lot of people (including me with my own money) bought the reels based on brand reputation.

I use and recommend one of the inexpensive Black Diamond range.   Most of their models offer infinitely variable brightness down to very dim, plus separate buttons for red or white light.

Best of all they can be set to always come on with the dimmest red light first whatever button you push - so no accidents! 

You do need to avoid the higher priced ones that have a battery check on starting up though.  This is because they light up an intense blue that'll ruin your dark adaption.  Additionally, those with the more costly Powertap feature can be knocked on accidentally.

For astronomy just look for models without a battery check and without Powertap technology.   BTW, the so-called Astro models aren't suitable for astronomy as they don't have a red light!

https://www.amazon.co.uk/Black-Diamond-Mens-Spote-Headlamp/dp/B07MP9KNNZ?ref_=ast_sto_dp&th=1&psc=1

https://www.amazon.co.uk/Black-Diamond-Unisex-Adult-Cosmo-Stirnlampe/dp/B07S2ZMGMV?ref_=ast_sto_dp&th=1&psc=1

Gorgeous!

No flattened edging on either my 8 or 10 inch OOUK Dobs.

In case it's relevant, the 22mm/70 deg Omegon Redline takes a Dioptrx to correct astigmatism.

IIRC, some of the others that are optically identical don't.  Don or anyone?

I agree with Don about it being a real bargain; in fact I preferred it to the much more expensive 22mm Nagler.

Mike,  if you can find this petition, I'll sign it.

Mike, has anyone looked into whether Thanet Earth are breaking their planning permission?

10 hours ago, 7170 said:

Thanks Steve (@Second Time Around

Are you comparing current status/forecast with conditions outside, or are you comparing the forecast from earlier in the day to actuals in the evening?

Copied from my first post on May 1st:

The forecasts were recorded roughly at sunset when I'd put my 10 inch Dob out to cool down if clear skies were suggested.  The accuracy was recorded over a roughly 30 minute period from nautical twilight when it was dark enough to observe.  This is approx 75 to 90 minutes later than sunset at this time of year.

I now use the app Sunrise Companion to sound an alarm at sunset.  If you long press on the date you also get the times of nautical sunset etc.

www.timeanddate.com also gives these times plus moonrise and moonset, but doesn't have an alarm.

The Met Office is slightly ahead, perhaps because of its consistency.  However, is this statistically significant?

Although I've an A level in pure maths and statistics it's so long ago that I've forgotten most of it.  To check whether the difference in accuracy of the forecasts is significant or not I seem to remember I'd have to do a student's t test (or is it a chi squared test?).  Anyone? 

However, the results are so similar that I think it safe to say that there's no significant difference between the various forecasts.

Short term vs medium term forecasts

What is interesting from my research is that there are 2 methods of deriving forecasts. 

The one most of us will be familiar with is the medium term forecasts that we see on the TV and websites.  These are computer models looking perhaps up to 14 days ahead.  They're "driven by powerful numerical weather prediction (NWP) systems. By solving physical equations, NWPs provide essential planet-scale predictions several days ahead. However, they struggle to generate high-resolution predictions for short lead times under two hours." (My bold italics.)

The other type of forecast is a nowcast.  "Nowcasting is a technique used for very short-range forecasting. The current weather is mapped and then an estimate of its speed and direction of movement is used to forecast the weather a short period ahead (assuming the weather will move without significant changes). It takes time to gather and map weather observations, so a short forecast is needed to outline what the weather is currently. Nowcasts can be used as a source of detailed guidance on the location, extent and timing of imminent, often high impact weather events."

"The Met Office produce a routine delivered service for T+0 out to T+6, for the United Kingdom, which blends our observations and UK Atmospheric Hi-Res model. At T+0 the blend is heavily weighted to observations and as time goes on the weighting of the UK Atmospheric Hi-Res model is increased, at T+6 the UK Atmospheric Hi-Res Model has the dominant weighting. The UK Atmospheric Hi-Res model is part of the Met Office flagship numerical weather prediction (NWP) model called the Unified Model. The resolution of the Nowcasting is comparable to radar data."

Nowcasting is of course what we need to decide whether to get our scopes out.  Unfortunately, nowcasting in its relative infancy.  AI is now being used to enhance its accuracy, for instance in tests that the Met Office is doing with Google's Deep Mind.  Hopefully, this will be of particular benefit to the likes of us.

In the meantime I'll continue to use these 6 cloud forecasts (with Good to Stargaze being added from next month).  

However, as I've mentioned elsewhere,  I also look at 2 other sites with satellite data.  The first is Zoom Earth for current cloud photos.  Unlike many sites it also shows cloud at night using infrared images, plus one can go back a long time.   Bear in mind though that low cloud and fog doesn't always show up on infrared images. But it often correctly shows that the only cloud in Kent is over our area, and that it's clear just a few miles away!

The other is Meteoradar as it extrapolates cloud satellite pictures to give nowcasts up to  3 hours ahead.   Unfortunately it does so only for daytime hours.  However, it's useful for soon after sunset, and also for solar observing.

How accurate are the current forecasts?

What will surprise many though is something I commented on in a topic where the OP was lamenting the accuracy of Clear Outside.  Even now, the current forecasts are pretty accurate.

Below are the figures for Clear Outside over the first 6 months of recording.  However, as I said, all the other forecasts will be very similar.

Correct 67%

Partly correct/partly wrong 29%

Totally wrong 4%

Above are the December results.  Click to enlarge the image. 

Yearly analysis to follow.

Outstanding!

19 hours ago, Mr Spock said:

Just remember, because of our clocks not being synchronised with the Earths orbit, nights have been drawing out a while while mornings are still drawing in. Overall we are round the corner though 

Yep, at our latitude  the earliest sunset was on December 12th, the latest sunrise will be on December 31st.   The winter solstice will be halfway in between.

Doesn't make any difference  to the almost perpetual cloud  though!

What an excellent report!

My own brain has frostbite and I may not be reading it correctly.  Does your OVNI-B not have gain control?

Here's the November results.

This has been the worst month for observing here since I came back to astronomy 3 years ago.  It was often clear at sunset, but night after night it clouded over before it got dark!   Frustratingly, the satellite photos showed it was often clear just a few miles away!  🤯

The only properly clear night we had was on the 2nd November, and December has started in the same way.

Sorry, I've got that a bit wrong.  My hands are playing up tonight and I thought that was the problem I'd found.

Rather it's that with the NPLs the eyecup is either up or down.  I prefer it in an intermediate position and the hairband allows this.  I find this especially important when solar observing with my Quark when eye position can be critical.

Thanks for flagging this up.

Having tried several Plossls in the 30-32mm range, your 30mm Vixen NPL is my favourite as it's so comfortable to use.  I like the twist up eyecup but it does has a tendency to slip down, especially with use. 

I've solved this by putting a hair band/elastic band round the barrel, and this holds the eyecup in the best position.  This will of course vary from person to person, but can be easily adjusted