Plossls On The Moon........

[cloudsweeper]

I recently got three Meade Plossls (two secondhand) to go with the TV 20mm, so thought I'd compare each with others EPs at similar mags.

3.35pm - Moon a slim waxing crescent, low south.  Set up the 8SE/GoTo (handy for tracking while doing the comparisons).  Got Mare Crisium (NE quadrant) in the EP, then chose crater Cleomedes to the north as my target as it has a series of three craterlets running across the central part of its floor.  By 4.10pm the sky was not as light, and anyway the Moon was bright enough and details were very clear in the EP.

Meade 4000 Super Plossl 32mm and Exp Sci 30/82, giving x64 and x68.  Two craterlets stood out more sharply at best focus with the Meade, and I thought it had the edge, although there was not much in it.  (The big ES showed the Ring of Fire Effect, and gave a slight orange hue to the Moon's surface, although these diminished as it got darker.)

Meade 3000 Plossl 25mm and Meade 5000 UWA 24mm, giving x81 and x85.  Again I was sure the Plossl had a slight edge, but that is not say the other one in either case was in any way poor.  Seeing effects were starting kick in, so I changed the EPs over frequently to give them each a fair chance against fluctuations.  (Once more, the wide angle EP showed a slight orange tinge at first.)

TV Plossl 20mm and Meade 5000 UWA 20mm, giving x102.  As before, not a huge difference, but I'd swear the Plossl again had a very slight edge with sharpness of fine detail (clarity of the craterlets).  At this mag, the southernmost and smallest of the craterlets was clearly seen with both EPs.

Meade 4000 Super Plossl 15mm and Exp Sci 14/82, giving x135 and x145.  Similar again.  The smallest craterlet was easier to make out with the Plossl.  

I was getting quite acquainted with Cleomedes by this time, so took it up to x226 - a great view at 0.27deg total field, but fine detail was lost to seeing.  Better at x203; pretty good at x185, 169.

At 5.00pm, the Moon was very bright and detail excellent, so I did all the comparisons again, and concluded that the Plossls DO seem to have the edge when it comes to showing very fine detail more sharply.  But only just!

A worthwhile exercise, finishing at 5.20.

Doug.

 

[Littleguy80]

Interesting comparisons, Doug. I really like my Orthos for fine detail. I do think the smaller FOV plays a part when targeting a smaller area. It brings a natural focus to the eye on the target. A smaller FOV needs less correcting so seems logical that a design could achieve greater sharpness across that smaller FOV.

[mikeDnight]

Sometimes it's nice to reevaluate some of the simpler designs of eyepiece. I'm a massive fan of the humble plossl/super plossl eyepiece,  and find that, although subtle, a well made plossl has an clarity and sharpness that can be lost in more complex wide field designs. It's great to read experiences like this, where careful, prolonged comparisons carried out by a careful and honest observer, brings this jewel of an eyepiece back into the lime light. 

[Merlin66]

Meade series 4000 "super plossls" - the early smooth sided, marked "Japan" on the black body were actually five element design "Masuyama clone?", the later versions marked "Japan" or "China" on the chrome barrel were four element similar? to the other Series 4000 eyepieces.

Which one did you test?

 

[johnturley]

I've kept several of my original Series 4000 (made in Japan) five element smoothside plossls, which date back to the 1980's, mainly for eyepiece projection photography (those with rubber eyecups probably won't fit in my eyepiece projection tube), maybe I should get them out for visual use as well.

John 

 

[Merlin66]

John,

If they are marked "Japan" on the black body, you may be pleasantly surprised!

 

[johnturley]

9 hours ago, Merlin66 said:

John,

If they are marked "Japan" on the black body, you may be pleasantly surprised!

 

Yes they are, I will have to give them another try and compare them with some of my wider field eyepieces.

I have the 26, 15, 12.4, and 9.7mm eyepieces, the 15mm used to be my favourite.

john