How To Calculate Image Jump

[@Beana52]

Ty sooo much your videos are helpful I am taking the ABO on Saturday, June 15th, at 230pm. I have been working on problems n taking practice tests. I am nervous about the exam. I pray 🙏 I pass it. Ty again for sharing all your knowledge and expertise.

[@suzannebeling3444]

So happy to have found these videos! Love them!

[@LaramyKOptical]

Thanks I'm glad you found them too! Have you seen the website? www.OpticianWorks.com? John

[@angelicramirez8098]

I actually have a patient that picked up there specs yesterday suffering from image jump and your right nothing you can do about it.

[@millennialdisposition1]

Just a question about the default segment hcm's listed at the end, I see it's 5mm but in the example earlier we calculated 3.5. Perhaps I am getting two things mixed up

[@LaramyKOptical]

Think of 5mm as a default or a rule-of-thumb where 3.5 was specific. Any difference is negligible. If a test question didn't provide you with 3.5 or some other specific amount then use 5 (or whatever is appropriate for the lens style).

[@skibickiadrian]

Thank You!! Greetings from Poland.

[@ItachiAli1993]

Am I missing something here? I've used a protractor and drawn a 28mm circle. I've got a D28 Bifocal and measured the straight top *Horizontally* which measures around 25.5 We know that the centre of the Segment will be at 14 since 28/2=14. From the straight top to 14 its 6mm and not 7.5mm. Am I looking at the Segment centre where as you are looking at the Optical Centre of the Segment? Your reply will be appreciated -UK

[@LaramyKOptical]

The "formula" if you will straight from Stoner's Optical Formula Tutorial is: segment center position = height of the segment - 1/2 the width of the segment. I think I cover exactly where that number comes from at about 7:45? The top of a lined segment is NOT at half the "circle" if you will. It is 3.5mm above it and that is where you are measuring to or from. That extra 3.5 mm of lens above the center is kind of everything where image jump is concerned. I think you might be over-thinking it a little? I do think it's covered in the video - maybe watch it again? Again image jump isn't an exact science and most test questions can be answered using rule of thumb measurements. I wouldn't let it keep me up tonight. John

[@ItachiAli1993]

@@LaramyKOptical Hi John. I have measured it myself with the help of a protacter. I am getting 6mm from the top of the segment to the centre for D28 and a D25. I am from the UK I don't know if its different in the US. My teacher also calculated for jump (D28) and used 0.6cm for hcm

[@LaramyKOptical]

@@ItachiAli1993 The "formula" says 1/2 the width of the segment NOT half the width of where you find the segment top or segment line. 17.5 - 14 = 3.5. Straight from the book: "As a rule of thumb, the OC of a segment is about: 2.5 to 6mm from the top of most flat top or straight top..." That says "about" it's a range, a rule of thumb, a close enough. It's a concept not a mathematical formula. If your instructor uses 0.6 then use 0.6. Absolutely nothing you can do about it 0.375 one way or the other. John

[@alice6494]

what value should be used when calculating jump for curve top (C28) seg?

[@LaramyKOptical]

Don't really see it listed anywhere but you could use the same as a ST. Might be wrong but I think curve-tops are obsolete?

[@luisgomez1211]

Hello Laramy, I'm looking your interesting theme, How To Calculate Image Jump...

[@williamchancellor6099]

Always great stuff , keep it coming!

[@LaramyKOptical]

Thanks!

[@ophthojooeileyecirclehisha4917]

I wish you accept my appreciation thanks

[@michelledasilva2639]

Thank you so much your awesome!

[@drjyotshna6221]

Sir? Can u just give a eg and explain image displacement and image jump ?

[@samdcuza7343]

Nice video

[@natelieherault4942]

Bless you for saying it: why are we spending time learning this useless formula? Lol. Sadly it’s been 3 years since this video is made and I am still learning about it in my course today… thanks for putting it so simply though :)

[@LaramyKOptical]

Be the change you want the world to be... Smile and nod your head but focus on what is important today. Focus on understanding free-form, compensated lens design and thinking like a business person. Focus on creating a selling experience where eyewear is a fun thing people want - not a medical device they need. If you haven't already sign up for OpticianWorks.com!

[@debbylariv]

:) Good job!

[@LaramyKOptical]

Thanks! Glad to see your name pop here! John

[@virajsalinda5150]

ST is 22. Now what is the calculation

[@LaramyKOptical]

Straight top 22 = still just use the 5 like you do for the other ST sizes or if it makes you feel better use 4 and you will be fine. Again - what difference does it make? You can't do anything about it... John